Thursday, 18 October 2012

Light Boxes

Description and Use
Light boxes are in many ways development from the glass easel. The glass easel was used in studios to wax up the painted glass and display it as it would be seen in a window. Sometimes the glass painters painted across all the glass at once, so this method enabled them to see the results immediately.
Nowadays people tend to use back lighting for these and other purposes, so the light box has become more popular. Some of the uses are outlined here:

The light box is very useful when tracing or altering designs. The back lighting enables you to use other paper than tracing papers to transfer the design elements. You can fold the paper along the lines of symmetry to check on how the lines match, or to copy the lines from one side onto the other side at the designing and cartoon stages.

The light box can help select glass colours either initially or when the main pieces have already been established. The combination of the glass over light shows how they interact with each other. At later stages when the main glass is cut, it can help avoid unwanted bright or dull areas.

Possibly the most common use is in cutting dark or opalescent glass. The additional light allows you to see the cartoon through the glass and so cut directly from the cartoon. This can be enhanced by blanking out the excess light from around the glass or cartoon.

The light box enables the arrangement of the cut glass pieces to be assembled to view the colour balance and have a virtual view of how the panel or window will look as a finished piece. An additional step toward the result is gained if each piece is outlined in white-board markers – use black pens - to represent the lead or copper foil and their widths. This stops the light between the pieces from causing you pupils to contract, and gives a more accurate representation of the appearance of the final pane.  White-board markers can just be wiped off the glass without using spirits.

The light box is important in painting. The back lighting shows the effect of the painted line or level of shading immediately. This allows adjustments to be made quickly and accurately before firing,

Depending on how the light box is built, it also can be used as display lighting. This can be as up-lighting or backlighting.


The top surface needs to be firm and scratch resistant. Toughened or laminated glass is good for this. The larger area covered, the thicker the glass needs to be, or there needs to be support under the glass to avoid breakage from pressure. The toughened or laminated glass resists breaking from dropping material onto the light box.

You need to have daylight corrected light sources for you light box, especially if you are doing any glass selection on it. Fluorescent tubes are easily available, but other light sources can be used. You need to have ventilation to allow the heat generated by the lights to disperse. Fluorescent tubes do not generate much heat and so are the common choice for lighting.

You need diffused, even light across the whole surface. This requires a diffuser and there are a number of solutions. You can sandblast the back of the top sheet, but I find this does not provide enough dispersion. You can sandblast both sides, which gives better dispersion of the light, but is difficult to clean and so needs another sheet on top. The best dispersion of light comes from using a sheet of opaque acrylic with about 80% light reduction. The difficulty with this is that it is flexible and needs support if any glass cutting is going to be done on the surface. I place the acrylic sheet underneath a sheet of 6.4mm laminated glass. This gives both solidity and dispersion.

Light is a central consideration in building the light box. The intensity is controlled by two things mainly – The number of lumens and the intervals of the light sources. The best way toward even light distribution even with good dispersion sheets, is to have multiple light sources. It would be possible to pack the box with light fixtures, but this is expensive and generates a lot of heat. It also may make the light too intense to be comfortable to work with. In general, fluorescent tubes placed at about 150mm centers apart will provide all the light you will need.

To make sure you get all the benefit of the light you need to build an enclosed box with ventilation holes or slots that is painted matt white on the inside. This allows the light to be reflected upwards through the surface without bright spots that can be caused with gloss paint.

You need to consider the size of the box in terms of surface area. This will relate to the space you have available and the scale that you work at. In addition to a separate surface the box can be an area of the work bench, or covered by a separate work board – whether permanent or temporary.

The height of the box will need to be considered. Will you be sitting or standing while working at the light box? It needs to be high enough in either case for you to maintain a straight back.

You need to consider the ability to screen parts of the light so the light is directed only at the work area. Large areas of light will overwhelm the glass, making it appear darker than the finished piece will actually be.

You need to think about the amount of flexibility your box requires. If you want to use it as part of your display equipment, it needs to be mobile and relatively light. This will interact with the materials to be used in construction.


Light boxes can be constructed in a variety of ways. The simplest to construct is the free standing, horizontal, single purpose light box.

You need to consider the size of the box in terms of surface area. This will relate to the space you have available and the scale that you work at. Having determined the surface area required or possible, you need to think about the height. The top should be of a height so you can stand or sit with a straight back while drawing, cutting or painting. This will vary according to your height and whether you will be standing or sitting. Typically these heights will be the heights of the benches and desks you already use, but you need to check again that you are actually working with a straight back, as this will reduce the fatigue you might otherwise experience.

Note that if the box is going to be sat at, it will need to be narrower to be able to reach to the opposite side. If you will be standing at the box, it can be at least half again as wide as the sitting version. A sitting version will also affect the depth of the box containing the lights. It may not be possible to have anything deeper than 100mm. This will produce some problems with the evenness of the light, but nothing that will make it unusable.

Then you need to consider the depth of the box. In principle, the deeper the box the better diffusion of the light. But there are limits. If the box is really deep, more lights will be required, and potential storage space is lost. I recommend about 150mm for the depth of the box. I then place the fluorescent tubes at 150mm centres across the box. It does not matter which direction they are oriented. That will be more determined by the available fittings and the dimensions chosen.

The flexibility you have in building your own box includes a number of things which could be constructed separately or in combination.

You can cover the light box with a sturdy work board to do all kinds of work on top. So this makes a combination light box and work bench. This top can be hinged so you don't have to lift it off each time you want to use the bench. It should have some support mechanism so it does not fall on your or your work. I have used a chain that allows the board to go back just beyond the vertical. These chains can sometimes get in the way of your work.

In addition to a separate surface the box can be an area of the work bench. The important element is that the rest of the surface of the bench should be at the same level as the light box top. Any variation runs the risk of breaking the glass you may be working on. The cover for this can be hinged to protect the surface when the light is not needed.

Often you will be working on pieces smaller than the illuminated area. It is possible to arrange things so that each light fitting can be turned on and off independently to allow light reduction or intensification as you need. It is simpler to have sheets of opaque card to place around your work area to reduce the extraneous light that will overwhelm the glass that you are selecting or painting, for example. In the case of too much light the glass or the painted lines and shading look darker than they really are as a result of your pupils contracting against the light.

You could add a variation to allow the light box to be used as a near vertical illuminated glass easel. This requires a set of hinges, a ledge on the hinged side and a support of some kind at the back, similar to a piano lid support. This is most useful in painting and in waxing up the pieces to view the whole panel before leading or foiling.

You need to think about the amount of flexibility you require the box to have when considering the materials to be used. If you want to use it as part of your display equipment, it needs to be mobile and so relatively light. This will interact with the materials to be used in construction. In this case you may want to make greater use of metals for their strength in relation to weight. 

 You probably will use opaque acrylic sheet as the surface. If you do, you will need to give it internal support to keep it from bowing. The best for this is another piece of acrylic – clear this time – glued to the top sheet and to the bottom of the box between the light fittings.

Working surface

I recommend your top should be 6.4 laminated or 4mm toughened glass for anything up to 610 by 1000mm. If it is larger, you should go to 6mm toughened, as 8.6mm laminated glass is pretty expensive. I suggest glass because it is strong, rigid, scratch resistant and easy to clean.

You can use a router to form a ledge for the glass to sit on. You can use a less machine intensive method, by nailing thin battens or quarter rounds around the glass. But the structure which confines the glass should be no higher than the glass surface. If it is higher than the glass, you can simply plane or sand it down. Insure there is no part of the fixings of the glass higher than the glass surface. This is especially important when cutting glass on the light box. If the surround is higher, you run the risk of breaking glass that is for one reason or another overhanging the edge. It also makes it easier to get the glass on and off the light box.

To get the appropriate diffusion you need to do more than sandblast the underside of the glass. While this will provide some diffusion, it is not enough. You can put another sheet of glass, sandblasted on both sides, underneath the top sandblasted sheet to provide good dispersion of the light. However, I have found a 3 or 4 mm sheet of white acrylic that is 70% -80% opaque provides the best diffusion of the light elements, even though it is more expensive than glass.

You also need to have a method to be able to get at the lights. This can be by having a removable section of the boundary. You can also make use of the ventilation holes, if appropriately placed, to lift the glass. A portion of the box sides can hinge to allow access to the lights through the side, although this is more awkward than fitting from above.


Light is a central consideration in building the light box. 

The best way toward even light distribution even with good diffusion sheets, is to have multiple light sources. I recommend placing them at the same distance apart as the depth of the box. It would be possible to pack the box with light fixtures, but this is expensive and generates a lot of heat. It also may make the light too intense to be comfortable to work with. If you can control the general lighting of your studio and you can turn it off or down, you will not need such intense lighting in your box.

An alternative, but more complicated method is to build the light box with baffles so the light is never directly under your work. Commonly, this would require the box to be built wider than the glass upon which you will be working. The light reflects from the sides and bottom of the box to give an even light. In this case, the single sandblasted surface would be sufficient to disperse the light and keep your eye focused near the surface of the glass or cartoon on which you are working.

You need to have daylight corrected light sources for you light box, especially if you are doing any glass selection on it. Fluorescent tubes are easily available, but other light sources can be used if they can be found in daylight colours. Fluorescent tubes do not generate much heat and are available in daylight corrected colours. So these are the common choice.

You still need to have ventilation to allow the heat to disperse, though. Ventilation can be provided in a number of ways ranging from drilling holes in the sides, to providing a slot in the side or bottom.

You need to have access to the light fittings to replace bulbs. It is easiest if this is by removing the glass top. You can provide tabs on or under the glass to lift it with, but these often interfere with other uses. You can use the ventilation holes if they are high on the box to stick a lifter under the glass to be able to grasp the edge. You can have a removable section to the beading that holds the glass top in place. You can provide a couple of finger holes at the top edge of the box to enable more direct lifting of the glass without disturbing any of the box fittings.

Another important element in getting the maximum amount of light out of your box is to paint the inside white. This should be a matte or at most silk finish. Any glossier finish will produce bright reflective areas. Shiny surfaces such as aluminium foil also produce these unwanted bright areas. In fact, a matte white surface gives more apparent light than aluminium foil in the light box.

The lights should be wired in series so they all come on at the same time. It is of course possible to have a switch for each fitting, to vary the intensity of the light for the work you are doing. This does add a bit to the expense, but may be valuable for your way of working.

Tuesday, 18 September 2012

Measuring openings

There are a number of measurements that are critical for a good design and a sound installation of window panels.

1. Tight Size: This is the full size of the glass opening with no allowances for expansion and contraction. In a wood or metal rebate frame one would measure from steel to opposing steel or wood to wood; in a stone groove installation, from the bottom of one groove to the bottom of the opposing groove. Depending on the size of the opening, this measurement should be checked in multiple areas; at a minimum at the top, bottom and middle horizontally and at the left and right jamb.

2. Sight Size is the daylight opening or the largest opening that allows light to pass through.

3. Rebate or groove details. With a rebate frame, the depth and the width of the rebate must be measured, as well as the interior return if round bars will be used (this dictates what size bar will fit and how long the bar should be). These dimensions are also necessary to determine the dimensions of the retaining moulding if one is to be used. If it is a groove, the depth of the groove and the width of the groove (measured from interior to exterior) are important.

4. Panel Size. This is the ideal size of a panel that will be installed into the opening in question. Typically, this will be a function of the tight size less 3mm in both width and height for a leaded glass panel, to allow for expansion and contraction. One must also recognize if the size varies throughout the frame and make allowance for this as well. With dalle de verre, you need a deep rebate or groove and allow at least 5mm in both directions for expansion.

5. The depth of the rebate or the width of the groove are also critical measurements. To allow for a proper installation, allow a minimum of 13mm to be added to the thickness of the panel to provide room for a proper putty fillet.

Based on comments from Art Femenella

When measuring older openings and especially doors, measure the diagonals in addition to all the other measurements. This provides a check of all your other measurements and also tells you whether the opening is a true rectangle or parallelogram.

Measuring a Rectangular Opening

Measure sight and tight sizes at top and bottom, and left and right. You should also measure the middle of the horizontals and verticals in addition to the details of the rebate.

Measure the diagonals to determine if the opening is “square” - all angles square. If these measurements are equal or +/- 5mm you can consider the opening to be a rectangle.

With bigger variations you may set out the cartoon using the measurements for the opening. Still, you need to know where the right angles are, if there are any, to be able to set out the cartoon to properly fit the opening. You can check for ”squareness” with a try square, although that is not completely accurate. If it is difficult to determine where the right angle(s) are, you need to take a template of the opening.


If it is not possible to tell where the right angles of the opening are, a template is called for. The material to be used for taking templates should be stiff, easy to cut, unaffected by moisture, and relatively inexpensive. This eliminates paper and some cardboards. If you can find stiff corrugated cardboard this works well. Mounting board works well too, but is expensive. Foam board is excellent, but also expensive. Hard board or other thin pressed board is inexpensive but difficult to cut with a knife. Thin plywood is also a good material for templates, especially if the opening is relatively regular. The more complicated the opening, the more cardboard, mounting board, or foam board becomes useful for its ease of shaping to the opening.

What ever material you use, you must mark which is the interior and exterior and for further checks, which is left and right. Fit this template into the opening to make sure it fits into the opening smoothly. This template will form the external extent of the built window when it is installed into an opening with a rebate.

Where the window is to be fitted into a channel, as in stone, you need to make the template of stiff material so you can determine the panel can be installed and that there will be enough of the panel within the stone channels to ensure the stability of the window in the future and still be able to manipulate the leaded panel into the opening.

Irregular rectangles

If you have found or can see that the opening is not a true rectangle and cannot determine where any right angles are, you need to take a template.

The objective is to make a piece that will fit into the opening without bending or being too small for the space. It will be the same size as the finished panel and so you will be able to put the finished panel into the opening without needing to trim or expand the panel.

  • First, trim the sheet of material you have chosen to use to a size a little larger than the measured size. Place the uncut side along one of the long sides of the opening. If the opening is a portrait format, place it on the right or left side as convenient to you.
  • Next, adjust the bottom by marking a line on the sheet. This is where a second person is very useful. One person can hold the sheet in place on outside of the opening and the other do the marking from the inside –in the case of the rebate being on the outside and vice versa if the rebate is on the inside. The marked line should be as close to the edge of the rebate as possible. The special case of an opening in stone will be dealt with separately.
  • Then take the sheet to a place where it can be safely cut. A long metal straight edge and craft or “Stanley” knife are often the best aids to cutting straight lines. Replace the sheet into the opening after cutting, and make any adjustments to the size and angles of the sheet at the bottom by marking and cutting as necessary.
  • When the side and bottom are adjusted, start on the other side. Proceed as for the bottom.
  • When the side is finished, start on the top.
  • Finally, present the whole sheet to the opening to make sure it slips into place with no snags, or bending of the sheet.

It may be that the opening is too large for a single sheet. In that case you will need to work with two or more sheets and try them together for the final fitting into the opening. You can put them together in the window. You can fasten them together with tape or other fasteners to make one sheet. You can also make two parallel lines both at angles and at intervals across the sheet so that when you get back to the studio you can exactly reproduce the full sheet by matching the marks and then firmly fastening them together. This makes transport of large templates much easier.

You will know that a panel made to a template made in this way will fit into the opening, no matter how irregular the opening may be.


Occasionally the window is circular and sometimes an oval. In both cases a template is important. The circle rarely is exact. Take the template in the normal way and then ensure you mark the verticals and horizontals for the opening. You often can use the jointing in the woodwork to help with these. Also mark any other reference points from the opening. Finally, mark which is the outside and which the inside.

This procedure will ensure that you will be able to fit the panel into the opening.

Round headed openings can be considered as a special case of a circle.

The horizontal you must find is the shoulder of the window. This is the place from which the curve springs on each side. The opening is generally vertical up to this point and then the curve begins. In stone, there is most often a joint at this point. This is often the case in wood too, if you can find the joint under the paint.

You need to make sure you have marked where this shoulder is on the template. You should indicate any reference points from the frame onto the template.

The join to the lower part of the window must be made obvious. Normally there will be an overlap between the lower rectangular template and this approximate half circle. You need to mark where this overlap occurs, if you do not fasten the two sheets together. This can be done by marking across the two sheets in a few places. This will enable you to join them exactly back at the studio.

Stone openings

When the opening is in stone, slight variations occur in the process of taking a template. The main difference is that the rebates are concealed. The rebates are slots into the stone. Thus, the template must slip into the slotted rebate. In these cases, the stiffer the material being used to take template, the better. Usually, thin plywood is the best material, as it has to be manipulated many times and in ways similar to the final panel.

Things are further complicated, as tracery is more common in stone than in timber framed openings. A complex opening shape may require two or more parts to enable the panel to be inserted. The taking of a template will help greatly in figuring out how the panel will be inserted into the opening.

Additionally, when the template is in position, you should mark the visible portion of the opening onto the template. Mark which is the inside and which the outside. Finally, mark on each template which side has the deeper slot as this will help in installation.

Saturday, 18 August 2012

Lampshade Processes

Design of Panel Lampshades
Design - Pattern/Cartoon Tools
Pattern Construction
Soldering 3-D Pieces
Reinforcing Lamp Shades
Vase Caps
Fibre blanket Moulds for Shaped Panel Lamps

Design of Panel Lampshades
Lamp Panel Dimensions

Lamp Panel Lengths
If you have determined the length of the shade and the diameters of the top and bottom, you can determine the length of the panel by maths or by a scale drawing.

Calculation of length
The maths is about right angle triangles. The dimension of the vertical part of the right angle triangle is the height of the lampshade. The horizontal dimension is the radius of the bottom minus the radius of the top. The length of the angle is the square root of the sum of the square roots of the vertical and horizontal sides.

E.g., a lampshade 200mm high with a 50mm vase cap and 400mm bottom width:
The vertical of the triangle is 200mm.
The horizontal is 400/2 = 200mm – 25mm (half the diameter of the vase cap) = 175mm.
The length of the panel is equal to the square root of the sum of the squares of the sides.

In this example, 40000+30625=70625 of which the square root is 265. So the panel is 265mm long.

Measuring the length
If you don’t want to do the maths, do a scaled or full size drawing. It only needs to be one side of the shade, but it can be the full shade.
Draw a vertical the height of the finished shade. Draw a horizontal line at the top and bottom of the measured vertical.

At the top mark off the radius of the vase cap on each side of the vertical. At the bottom also mark the radius of the shade on each side of the vertical.

Join the two end points of the horizontal lines on each side of the vertical.
Measure this diagonal line to determine the length of the panel.

This drawing method does have the advantage of allowing you to see the angle of the proposed shade and adjust it if necessary.

Calculating the top and bottom widths
When doing custom lamp sizes is not too hard to calculate the panel sizes. You need to remember the value for pi (ca. 3.1417)

Start with the bottom diameter you want. Multiply it by pi. Divide this distance by the number of panels required for the lamp. This gives the size of the bottom of the panel.

Worked example
Bottom diameter: 200mm
Top diameter: 50mm
Panels: 8
Pi: 3.1417
Glass thickness: 3mm

Formula for bottom: dia. * pi = circumference / no. of panels = width of panel
Bottom diameter: 200*3.1417 = 628mm/8 = 79mm for the base of each panel.

Do the same for the top, but make one more calculation. As the top has to fit into the size of the vase cap, you need to take account of the thickness of the glass. So, subtract twice the thickness of the glass (the glass thickness is on both sides of the circle) from the diameter of the vase cap and use that as the diameter for determining the width of the top of the panel.

Worked example
Formula for top: dia. - glass thickness *2 * pi = circumference / no. of panels = width of panel
Top diameter: 50-6= 44 * 3.1417 = 138mm / 8 = 17mm

Determine the shape of the panel
When you have determined the widths of the top and bottom of the panel, you are ready to draw up the shape of the panel. Set up a horizontal line that is the calculated width of the bottom of the panel. Divide it and draw a vertical from the centre of the line. This line should be as long as the panel you are making. This is determined by the method outlined in the Panel Length tip. At the top of the vertical line draw another horizontal. Measure off one half the calculated top distance on each side of the vertical line. Join the points on the lower and upper horizontals to give the shape of the panel.

Design of shaped Lampshades
Pattern/Cartoon Tools

The items you need to have for creating your own pattern are not extensive or unusual. The essential ones are:
Craft knife or razor blade
Baby/talcum powder
Fine pointed felt tipped pen
Highlighting pen
Carbon paper
Drawing paperMasking tape
Lampshade form
End/vase cap

Pattern Construction

The first stage of the process is to prepare the design on flat paper. The second stage is to get the design onto the prepared mould and make adjustments to give a balanced and pleasing appearance

Trace the pattern onto the template
Prepare the lampshade mould by covering it in masking tape.

Take your design elements and trace them onto the masking tape on the form. The use of carbon paper enables you to put the design element and trace right on top of the taped mould so that the image is transferred onto the tape.

An alternative method is to use a pounce wheel to perforate the design element. The element is placed on the form and dusted along the perforated line with a bag of dark coloured powder such as powdered poster paint. This will leave a temporary trace on the form that can be changed easily, but needs to be pencilled in before too much other work smudges the shape.

Do this tracing with each design element, flipping and rotating them around so that you don't repeat any element exactly. Fill up major sections of the form using this method. Drawing the main features first and filling with the minor elements helps provide a pleasing composition.

Fill in background areas
Now that the key design elements are onto the masking tape template, create background pieces by linking your design elements. Use pencil, since you will probably need to do corrections. Remember, avoid creating large horizontal pieces. Larger vertical pieces are usually better. However, try to keep all the pieces of similar size.

Correct any pieces and number them
Once you are satisfied with the design, go over every line with a fine felt tip pen or other ink pen so that each is clear and distinct. Number each piece and mark colour and glass textures as necessary.

Based on work by Christie A. Wood, Art Glass Ensembles


Cut the finished template into sections (if you are using a 360 degree form)
The masking tape template will need to be cut off the curved form and laid out flat. This is easier to do if you can logically separate the template into smaller sections. To do this you need to find lines running almost vertically from the top to bottom of the template. Mark these separation lines in a different colour. Also label each section.

Remove the template(s) from the form and press it out flat
Take a craft knife or razor blade and trim away excess masking tape from the end cap mark. Do the same for the bottom edge. Carefully remove the excess.

Prepare a section of your work surface by sprinkling some talcum powder on it, and onto your hands as well. This will help keep the sticky side of the masking tape from sticking where you don't want it later.

Using a craft knife, slice through the middle of each separation line that you marked in a special colour. Try to stay in the exact middle of the line. Be careful that you don’t tear the underlying masking tape, or pull it away as you cut through the line. Do this with each separation line.

Starting with the top edge, use the craft knife to gently pull the masking tape template off the form. If the masking tape starts to separate, stop and repair it. As each section is taken off the form, put it sticky side down into the talcum powder and press it flat. Do this for each section.

Scan/copy the template(s)
At this stage you can scan each section into Glass Eye or other image software. This allows you to:
  • select and change colour/glass choices very easily
  • print out or email colour proofs to the client
  • keep them in an electronic form for future reference or manipulation

You don't have to scan your pattern, but you do need to make at least two copies of the pattern.
  • One copy is fastened back onto the form so that you know where to put your glass pieces.
  • The other copy is cut out using pattern shears (the three-bladed scissors) and glued onto the glass for cutting.
Based on work by Christie A. Wood, Art Glass Ensembles

Soldering 3-D pieces
When soldering 3-D pieces together, first tack the panels together with a single tack at each end. If it later turns out that there is an alignment problem, it is much easier to dis-assemble a few tacks, with a piece of paper inserted into the space between the pieces of glass and moved up into the molten solder while your iron is at the tack joint. The paper will strong enough to move through the solder, separating the two piece of glass.

Once your 3-D piece is tacked together and looks OK, turn the piece over on its side, and, using 50/50 or 40/60 solder, fill in the inner seams, moving the piece around. Be careful to support the piece with boxes or blocks and by holding it at the top part above where you are soldering, to prevent the piece collapsing.

Once the inside of the piece - say a panel lamp - has been soldered smoothly with the solder with a higher lead content, turn the lamp over and prepare to do the outside. Arrange boxes or similar supports to prop the lamp upon, and orient it make a level joint to solder. Using the 50/50 or 40/60 solder again, fill in the seam. It doesn't have to be perfect, at first. Do all of the seam filling first, to ensure the stability of the piece. Then go back with 60/40 – the higher tin content - solder and, again making sure the lamp seams are level, finish by smoothly soldering each seam.

Reinforcing Lamp Shades

When constructing large or heavy lamp shades, reinforcement needs to be an integral consideration in the construction. With panel lamps the reinforcement is relatively simple – it can be along the seam lines. In fact, if you do not bevel your glass at the panel edges, it can be in the upper seam lines, as the solder filling the open joint will cover the wire. If the panels are bevelled, the wire can just go on the inside along the joint.

The wire should end at the edge of the bottom of the skirt so that it does not extend beyond, but will still be in contact with the edge reinforcement. The upper wire should extend beyond the top of the shade, so that it can be soldered to the vase cap. If there is not one, the wire should be dealt with as for the bottom, and there should be edge reinforcing.

The wire that is easiest to use is single strand copper or brass. It should be of a size to fit at the bottom of the “V” of each joining panel.

The bottom edge of a lampshade can be reinforced in various ways depending on the shape.

If the bottom edge is straight or only slightly undulating, brass “U” channel or other hard metals can be used.
Where the edges have points or acute angles on the edge, you need to use copper or brass wire. Again, single strand wire is better than twisted. It needs to be thin enough to conform to all the angles of the edge.

Choose a starting point. The best is where a reinforcing wire comes to the edge. Also you can begin at the base of an internally facing angle, so there is no opportunity for a wire end to stick out.

Tack solder or sweat the wire to the bottom edge of the panel where you decided to start. Then bend the wire to conform to the angles and curves of a portion of the lamp. If it is a panel lamp, bending the wire to conform to the edge of one panel at a time should be enough. Tack or sweat the wire to the panel at the bottom of each inward facing angle, as it is more difficult to keep the wire down in those areas than on outward facing angles. Once you have tacked the wire all around the panel, you will come to the start where you need to make sure you do not un-solder the beginning of the wire while trying to fix the end. It can be a help to overlap the end of the wire along the beginning. Alternatively, you can take the end up along the vertical reinforcing wire and fix it there.

Now you can begin to run a bead along the bottom edge of the panel to cover the wire. Make sure the wire and foil are both fluxed all along their length. Then orient the soldering surface is horizontal as you apply the solder. Move the shade frequently to keep the area to be soldered horizontal to avoid the liquid solder running into uneven lumps.

Vase Caps

Attaching the vase cap securely is important as often the whole lampshade hangs from the attachment points between the cap and the solder seams of the shade.

Once you have assembled the shade and tack soldered it together, perch the vase cap on the top covering the opening and apply solder so it joins the vase cap with the solder seams. It is a good practice to turn the lampshade over and apply solder from the seam to the inside of the vase cap. A good strong joint at each seam will be perfectly strong enough to hold the shade in position for many years.

Vase Cap Fitting

There are at least three ways to get the right vase cap size. 

Make up your shade in a cardboard mock-up. Use 3mm thick card or foam board to represent the glass, as the thickness of the glass is important in determining which vase cap is the correct size. Try your vase cap against the cardboard model, then if you need, alter the pattern so the glass pieces meet at just the right place to make the lip of the vase cap fit just over the top of the glass. You can do this by either shortening or lengthening the pattern a little at the top edge. 

The second also involves making a cardboard mock up. After making this maquette, choose a vase cap that overlaps the top opening, covering all the edges. 

The third option is to use two vase caps, one above and one below the opening to clamp them together trapping the edges of glass between them. Use a furling and lock nuts with no solder at all to hold the lampshade together.

Tinning brass vase caps

Tinning brass vase caps can help in obtaining a secure joint without long dwells at each joint, risking the overheating of the glass.

Heat your vase cap with a torch of one kind or another. You can heat until it becomes a dull red. The quickly brush or rub (with a cloth) flux onto the inside and outside of the rim of the vase cap. Apply a little solder to the fluxed area while everything is still hot. This will tin all the areas where the flux was placed.

This method gives a strong solder to solder joint that requires much less time when soldering the cap to the rest of the lamp shade.

Tinning Brass
Brass transmits heat much more quickly than lead, so a considerable length or the whole of the piece, e.g., a vase cap needs to be heated to avoid the cap acting as a heat sink and so not allowing even tinning of the object.

When tinning any brass pieces, like a lamp cap, rub it with fine grade steel wool (often labeled 000) until bright, then wash the residue off and dry. Apply flux with a fresh flux brush, and hold the piece with a pair of pliers.  Brass transmits heat much faster than lead or solder, so this is a precaution against getting burnt.

At this point you can heat the brass or vase cap with a low heat blow torch to warm the whole piece. When warm, turn off the blow torch and begin applying the solder with the soldering iron.  Touch the piece with your hot soldering iron, pause and then start moving the iron slowly and smoothly over where you have applied the flux, applying a little solder all the time.

Alternatively you can work without the blow torch. Apply a bit of solder to the tip of the iron. Touch the piece with your hot soldering iron, let the piece heat up a little, and then start moving the iron slowly and smoothly over where you have applied the flux.

When the whole piece has been covered, wash it, dry, and then inspect for any missed spots or unsightly solder blobs. Apply a little bit more flux and touch with your soldering iron. If you are doing a lot of this kind of work, an 800 degree iron tip will speed up your work.

Fibre blanket moulds

It is possible to make moulds from fibre blanket which will last for a number of firings if handled carefully.

Pre-wetted fibre blanket is available - Moist Pack is one brand name.
Or you can make the mould yourself from fibre blanket and hardener. You need:
- ceramic fibre blanket. It should be 3 mm or thicker, but 25 mm needs to be compressed when wet. It is possible to use two layers of 3 mm fibre blanket, but they do not stick together well unless thoroughly wetted.
- colloidal silica - often is called mould hardener. Paint this onto the fibre blanket liberally, both sides if possible.

You must protect the master with cling film, Vaseline, or other waterproof separator. Be sure about whether you want a draping or slumping mould, as the inside needs to be smoothest for a slumping mould and the outside smoothest for a draping mould.

Press the wet fibre blanket to the master. Then let it dry for a couple of days to become stiff enough to remove from the master. Let the negative dry for another period.

If you are short of time, you can dry it in the kiln at about 200C. Once dry, you can then fire to a minimum of 760C to harden the mould. The point is to get the glass which has been in suspension to soften and stick together. Upon cooling the mould will be hard, as it is held together by the glass structure within the fibre blanket.

Then sand to smooth. Wear a dust mask during this process and do it out doors if possible. Otherwise a well-ventilated room is necessary. If unhardened blanket is exposed during the sanding process, soak in the colloidal silica and dry and fire again. Alternatively you can make a paste of the sanded material and the hardener and apply it to the mould before firing it again

Before use, the mould needs to be kiln washed, or have alumina hydrate powder sprinkled over mould, otherwise glass will stick to mould.
With delicate treatment, the mould can be reused many times.

Example of a lamp panel mould from fibre blanket

Wednesday, 18 July 2012

Installation of Glazing Bars

There are a few tips that concern the installation of glazing bars into wood frames. An important element to understand is that the purpose of the bars is to protect the panel from horizontal wind pressures on the window, not to lift the panel or in any other way strengthen the panel vertically.

Glazing bars are normally round. The diameter depends on the span of the opening. For openings of about 600 mm a bar of 10 mm will be sufficient, up to 900mm needs 12 mm at least. Of course, the depth of the rebate will be a major factor, as there needs to be some wood remaining on the frame to hold the bar secure.

In some cases a large bar is indicated, but there is not enough depth in the rebate to take such a diameter. These are the cases where the bar is heated and flattened so it can be inserted into a slot, rather than a round hole.

The holes on one side should be at least 5mm deeper than the other. For a really secure attachment one side should be at least 15mm deep and the other 10mm. This allows a significant amount of wood to seat the bar. The bar should be at least 10mm longer than the opening is wide. And the deeper hole allows the bar to be slipped deeply into one side and then slid back to seat in the more shallow hole.

The hole you drill should be 1mm larger than the bar diameter. This will make moving the bar easier. Additionally, the ends of the bars should be filed to remove any roughness. Also, greasing the ends of the bar with tallow or candle wax will ease the movement of the bars.

If the bar is to be installed inside sash windows you can ease the installation by determining the height of the hole to be drilled. Present the panel to the opening and mark the frame where the bar is to be attached to the panel. Drill the hole so the edge of it is flush with the rebate but no deeper than the outside of the opening. This allows you to use a chisel to open the hole enough to allow the bar to be placed in the socket now prepared from the outside. In these cases the bar needs to be no longer than the opening.

The installation should be completed by forcing putty into any gaps left between the bar and the hole. This will stiffen and help to firm up the bar’s attachment to the frame.

Tie wires for glazing bars are to keep the panel from rebounding due to wind pressures on the window. There also is some pressure created within the house by the opening and closing of doors, although this is minor in comparison to the weather.

The tie wires should be securely soldered to the panel at solder joints. Placing ties elsewhere leads to the tearing of the lead. The soldering of the tie wires requires more heat than simply soldering the lead joints. The tie wire needs to be heated enough to melt the solder of the joint to which it is being attached. Then an additional dot of solder needs to be added so that the wire cannot simply pull out from the joint by being only sweated to the joint.

When installing tie wires for panels that are to sit on top of one another, the wires should have a small loop created where it is soldered to the joint. The wires should be soldered at the loop end to the panel joints and extend down or up along the panel. On the other panel which meets it, the same procedure should be followed. In these cases the minimum amount of solder should be used to avoid making the panel too thick at the point where the upper lead comes down on the lower.

At installation, when the panel is fully seated in its opening and fastened by nails or sprigs, pull the tie wires out at right angles right at the edge of the solder attachment before twisting the wire. Do not use any more than firm pressure. Then you are ready to cross the wires over the glazing bar. This ensures there is no excessive give in the copper tie.

On panels sitting on top of one another, the wires on the lower panel should be passed behind the bar and up before turning over the bar. The wires of the upper panel should be passed below and behind the bar before turning up over the bar. The protruding wires should then be twisted as for single panels.

Do not over tighten the tie wire twist. Only twist until snug against the bar. Then continue to twist the loose ends until you have them a satisfactory length. Cut off the twist rather than the tail ends to provide a neat finish. Then tuck the twist under or over the bar, just as you desire.

Monday, 18 June 2012

Cementing Leaded Panels

Cementing panels is as old as leaded glass - over 1,000 years - so it is a time-proven process using simple materials. The object of cementing is to make a leaded panel weather and water tight and sturdy. It can be messy and dusty, so putting on an apron and a dust mask are a good idea.

Part 1: Cement

You can make your own lead light cement as the materials are fairly common and safe to use.

7 parts whiting/chalk
1 part boiled linseed oil
1 part mineral spirits (turpentine or other)
(All of the above measured by volume)
1-2 Tablespoons lamp black or other colorant – black poster paint, acrylic paint or oil paint
Tools and Materials for Making Cement

The mixer should be capable of mixing bread or similar stiff dough. The existence of a dough hook among the beaters is a good indication.  Also it is best if the bowl is rotated as this makes for much easier and more fully mixed cement.

Add the whiting (reserving about one quarter) to the linseed oil and mineral spirits. Mix this well, by hand or with a domestic mixer capable of mixing bread dough. When these are mixed thoroughly, check the consistency. It should be like molasses on a cold morning - barely fluid.  At this point, add the colourant, so you will know the current colour and can adjust to make it darker.

Add more whiting as required to get the consistency you want. Experiment a little to find what suits you best. If you have to deliver the panel quickly, for example, you need to increase the proportion of mineral spirit. The mineral spirit evaporates relatively quickly, leaving a more rapidly stiff cement.

Being mixed

Note that the cement is nearly finished mixing as the ribbons of material are forming in the above photo.

Mixed and ready for application

When fully mixed the cement should only slowly drip off the mixer beaters.

You should make only what you will be using on the current project, as the whiting separates from the linseed oil and spirit relatively quickly. The commercial cements have emulsifiers to keep the whiting from settling and so extend the life of the product. Since making your own is cheap and quick to make, there is no saving in making a lot.

Part 2: The Start

Start on the side that is already facing up after soldering. This normally will be the rough side. This way you do not have to move the panel much until it has stiffened with the addition of the cement.

Starting with the rough side enables you to cover all open bubbles, rough glass (waffle, ice, etc.) and all painted glass with masking tape before you start. Put the tape over all the relevant areas of the panel, then use a sharp craft knife to cut the tape at the edges of the came. The cement will go under the came, but not into the texture of the glass. This will make the clean up of the glass much easier after cementing.

Adding the cement to the panel

With the panel on the bench, put a dollop of cement on the glass and rub it in all directions with a stiff, but not hard, bristle brush to force it under the lead. 

Scrubbing the cement under the leads

Adding whiting

When the cement has been pushed under all the cames, but with a slope of cement showing, spread a little fresh whiting or sawdust on the panel and gently push it against the cement under the leads. This begins the setting process and keeps the spreading cement from sticking hard to the glass or bench.

Adding cement to second side

Turn the panel over to cement the second side the same way as the first. If the panel is a large one, you may want to use a board to support it in these early turning stages. No gaps can be tolerated in the cementing. Cement leaking out the other side is good evidence that all the gaps between the glass and the came are filled. Again, after cementing, sprinkle new whiting/sawdust over the second cemented side and rub it gently into the exposed cement.

Scrubbing second side

Adding whiting

An illustration of the need to ensure the cement is well scrubbed under the leads comes from an occasion I had to repair a panel made by a client's friend several decades ago.  It was cemented by pushing commercial putty under the leaves of the leads.

This photo shows how the putty filled the space above and below the glass but not between the glass and the heart of the came.  It also shows the putty missing from the corners of the glass. 

The question may be asked about what is so important about a bit of putty missing from the edges of the glass, it is sealed along the leaves of the came. Yes, this style of cementing will seal the panel from the weather for a time. But had this glass been a window instead of hung inside, it is questionable as to how long it would have been until it began to leak - possibly only 20 years after being made. Certainly as the putty begins to break down, the moisture will rapidly find its way into the inside.

The only way to be certain that the panel is completely weather proofed is to use brushable cement. The cement is pushed under the leaves of the lead with a stiff brush. You know the fill is complete by the cement oozing out of the other side.

Part 3: Setting Up the Cement

After the pushing the cement under the cames on both sides, flip the panel over and begin a firm rubbing to push cement into the gaps between the lead and glass. Sprinkle the used dust from the bench top over the panel and rub in all directions. This begins to set up the cement by helping to provide a stiff skin over the more fluid cement. Brush until the whiting is largely off the panel. Turn the panel and do the same for the second side. Several applications of whiting/sawdust are required to give a sufficiently thick skin to reduce the amount of spreading, leaking or weeping cement.

Once both sides have been done a couple of times, begin to concentrate the brush strokes along the lead lines rather than across. This will begin the cleaning phase and also begin to darken the came. Repeat this on the other side.

After a few turnings, most of the cement will be cleaned from around the leads. Don’t try to get all of it away, you will need that colour for polishing. The glass will be shining, and any felt tip marks you made on the glass will have gone too. Clean up the dust from the panel and bench in preparation for polishing.

Part 4: Polishing Lead Cames

Use a soft brush to polish lead came. Don't pick out the cement until the polishing is done, as it provides the colour for darkening and polishing the lead and solder joints. 

Polishing with softer, finer bristled brush

The action with the polishing brush should be gentle and rapid, much like polishing shoes. If the shine does not come, you can use a very little stove blackening (carbon black mixed with a little oil) If you use a lot, you will have a big clean up job. A little stove blackening spreads a very long way.

Picked out, but not swept, polished inside

Before turning the panel a final time, put down paper or cloth, to avoid scratching the solder joints while polishing the other side. The result should be shiny a black came and solder joints that does not come off the way a final buffing with stove blackening does.

Finally, pick out any remaining cement.

Picked out outside

Resting, inside up

Rest horizontally with weather side down for traditional installations. If the panel is going into a double or secondary glazed unit, you may want to reverse this. The reason for having the smallest exposed cement line on the outside is to allow the water to run off the window with the minimum of area to collect. In a sealed unit or for secondary glazing, you may want to have the smallest amount of cement showing inward for appearances, as there is no weathering reason for the traditional method.

Rest for a day. Pick out the cement again. If the cement was stiff enough, there should be no need to do any more picking at the cement after this.


Use stiff, but not hard bristle brushes for cementing. Nylon scrubbing brushes have a good stiffness without being too hard. Some natural bristle brushes are very hard and scratch the came excessively. In general, moderately stiff brushes with about 35 mm bristles are fine for cementing. As they do not last very long, they should be cheap, but with firmly attached bristle bunches.

Cleaning the brushes is very simple. The action of rubbing the cement under the leads with whiting causes a natural cleaning action to take place. As the bristles flex back and forward over the came, the cement is forced upward toward the handle, and then outward between the bristle bunches. Only a little effort is required to finish the cleaning: push a rounded stick between the bunches to move out the remaining cement. You now have a clean brush for the next job.

The alternative is keeping the brush in water, but this presents the problem of getting rid of the water (oil and water do not mix) before beginning to cement. As the water will emulsify with the linseed oil, it will be carried into the putty, leaving gaps in the cement when the water eventually evaporates. The cement will eventually harden, even though in water, as linseed oil cures by creating an organic polymer through oxidisation. It can also rot the wood handles.

Keeping the brush in mineral spirits does keep the brush flexible but requires drying/evaporating the spirit before beginning the cementing to avoid the residue of the spirit creating cement that is too thin at the start. This can be a really messy problem!

If you choose the “dry” method, it is important to keep the brushes free of hardened cement as it will scratch the leads badly, if not the glass also. Most brushes will only last 5-10 uses, and as they are not expensive, should be easy to throw away.

Polishing brushes should have more and finer bristles than cementing ones.  They can range from the very soft shoe polishing brushes to medium firm.  Many stained glass suppliers sell these, but a good shoe polishing brush kept clean will last for years.