A question has arisen on how to put together a design of pieces for a lamp, but only one layer thick, because 3mm is as thick as the fittings will accept.
The design has no overlaps, so it is a series of butted 3mm thick pieces. Damming has not been successful in keeping the parts from retreating from one another. This means that making the design as a single layer will not be successful.
The problem is how to make a two-layer piece that will be able to fit into 3mm fixings.
Design on oversize 3mm base
One way to overcome the fixings’ limitations is to make the bottom layer larger than the top. The bottom can be any colour you choose. Make the design on top of that.
The designed pieces will need to fit snugly beside the fittings. However, the bottom needs to be cut larger than the final size, as it will retreat and become smaller during the firing. About 20mm larger all around will usually be enough extra for ease of cutting down. If you fire with a larger base piece, you can cut it to size after firing, so it will fit the width of the opening and still fit inside the 3mm fitting space. This will make your design proud of the fittings. This may, or may not, be possible for the lamp’s fitting design.
Maybe that is not the only way to look at the problem. There is another way. It is essentially the opposite of the first approach.
Make the top layer larger than bottom. The design will be on the top still, but with larger than final dimensions to accommodate the reduction in size of the single layer. The bottom layer will need to be small enough to fit within the space between the fittings of the lamp.
To keep the unsupported parts of the upper layer in one plane, support the larger upper layer with 3mm fibre paper. Coat the fiber paper with boron nitride or cover with powdered kiln wash, Thinfire or Papyros to get a smoother back. When fired, cut the piece to size. If you like to score on the smoothest side, you can support the edge with the fibre paper or other 3mm substance. If you are confident, you can score on the back with no special support.
These are two approaches to making a piece to fit in a 3mm channel. This will apply to insertions of fused glass leaded glass panels, as the came is designed to accommodate 3 mm glass.