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

1 comment:

  1. Thank you for sharing this information, Stephen. I find it very interesting and I think it is going to be very useful. Edith