Stainless Steel Stringer Pots

Credit: Paul Gardner httpswww.facebook.com

 It is a consideration in stringer and murrini work that the pot be re-usable. This has led to the development of stainless steel square pots.  The thorough cleaning of these is difficult even with a lot of banging. Containers with removal bases have been developed as a result.

 The importance of a container with an integrated bottom is to ensure the glass is contained within the pot. To be reusable, the pot can be lined with fibre on sides and bottom. However, fibres can be drawn from the lining into the stream of glass.

Credit: Paul Gardner

 If you have a stainless-steel square with a removable bottom, the pot can be cleaned more easily and does not need the fibre lining. It also allows easy switching of bases with different hole sizes and shapes.

 However, some people have had the difficulty of the glass flowing out between the sides and bottom of the pot and onto the floor of the kiln. Glass is heavy and can float the much lighter stainless steel off the base, allowing the glass to flow sideways as well as through the hole in the base.

 This indicates that the stainless steel square should be weighted down. Placing kiln furniture on top of the pot can avoid it being floated off the base piece. These can be dams made from kiln shelves, dense fire brick, a small shelf, ceramic tiles, or other kiln furniture. Putting the furniture on two opposing corners will be enough to counteract the floating of the pot and still allow radiant heat to reach the glass.

Pots can be made from refractory materials too, such as vermiculite.

Liners for pots

Slumping Tack Fused Glass Stringers

After you have tack fused your stringers, you will have a fragile blank, about four stringer layers thick. This will need to be handled gently and watched carefully during slumping.

When you slump, you should fire very slowly. Although thermal shock is not likely, the thin pieces have a tendency to crack when they bend into the mould. A safe firing schedule would be to advance at no more than 150C/hr to 540C, then increase the temperature at about 55C per hour toward 677C. Keep watching until the piece slumps into the mould, then advance to the next segment of the programme and anneal as usual for 6mm thickness.

For your first attempts, it's a good idea to use a shallow mould. After you get a feel for the process, you can achieve deeper slumps.

Further information is available in the ebook: Low Temperature Kiln Forming.

Tack Fusing Glass Stringers

The most time consuming part of tack fusing stringers is laying the stringers out. Most stringer bowls start with around four layers of stringers. The stringers need to be arranged in rows. It is often necessary to use a small amount of glue to keep the stringers in place as they are arranged. Some people glue the stringers directly to a piece of paper (normal or thinfire) to make them easier to arrange.

Making an 450mm square piece will take around six tubes of stringers.

If you want a piece where the individual strands of stringers are visible rather than fully fused, you will need to fire to as low a fusing temperature as possible. The precise temperature will, of course, vary by kiln. Most kilns will achieve tack fusing results in the range from 700C to 730C. Fire as quickly as you would like to around 675C, then increase the temperature very slowly, 50C per hour or less. You need to watch closely as the temperature approaches 700C. When the top layer of stringers begin to sag, start cooling the kiln. Firing too high will lead to a flat piece with no feel of the individual stringers.

Further information is available in the ebook: Low Temperature Kiln Forming.

Stabilising Stringers

Stringers and rods never seem to stay where you put them.

• Glue them and they move after the glue has burned away.  
• Grinding a flat side to them seems a lot of work.  
• Easier, is to put them in the kiln and take them to a tack fuse to give a flat spot. But that takes a lot of kiln time.
• For stringers you can put a kink or curve in it by heating over a candle.  Rods require more heat than that. Of course, this is of no use for straight lines, and takes additional time.

A simple method which can be used with a tiny amount of glue, or not, is to add clear fine frit around the stringers and rods. This is enough to keep them from moving once the glue is gone due to the heat.

Assembled panel by Kathleen Watson with the stringers surrounded with fine clear frit which can be seen as white

The frit should be put on the assembled panel once it has been moved to and placed in the kiln.  Any movement will disturb the frit and defeat the purpose of keeping the stringer or rod in place.

The fired result

This was fused to a rounded tack fuse and no signs of the clear supporting frit is visible.

This is a quick simple method to stabilise rod, stringer and other small items that may shift in the firing.

Flattening stringer

Placing stringer is often difficult. Not simply to put it into place, but to keep it there. People tend to hold the pieces with glue. However, the glue burns off before the stringer is anywhere near even tack fusing temperature. This allows the stringer to roll. Also an excess of glue will boil off during the heating and so move the stringer even more than gravity will. Two methods are effective in reducing the ability of the stringer to roll, by flattening one side.

Grinding

One method used by Bob Letherbarrow is to hold a stringer that is much longer than needed against the glass grinder bit. Use your thumb to hold the stringer against the bit. Slowly pull the stringer between the bit and your thumb or finger, using light pressure, to hold the stringer against the spinning grinder bit. This will slightly flatten one side of the stringer.

Firing

Another method is to place the stringers on a prepared kiln shelf, making sure they do not touch. Take the temperature quickly up to a tack fuse, soak for a few minutes and turn off. This will take only an hour or so and enables you to prepare a number of stringers with a minimum of effort.

In both cases, cut the stringer to the length needed and place on the glass with the flat side against the glass. Glue it very lightly to hold it in place while moving the piece to the kiln if it is absolutely necessary. When the glue burns off the stringer should not roll around. It is best, of course and if at all possible to place the stringers in the kiln, so no glue is needed.