Carved Fibre Moulds

The question of whether you can use carved moulds more than once will arise.

This refers to moulds made from refractory boards or materials.  Once fired, refractory boards and materials become more fragile as they have lost their binders.  If the carving is simple with lots of support, and the mould is kept supported in a container of some sort, rigidising is not essential.  The life of the mould may be short though.

To make a longer lasting mould, you can rigidise the refractory material using this method.  This can apply to board as well as blanket.  The process will make a much longer lasting mould that is light weight, and is not affected by rapid changes in temperature.

Do the fibre moulds need kiln wash?

This depends on both the nature of the material and whether hardened or not.  Refractory fibre boards – often called ceramic fibre – do not need kiln wash to separate the glass from the mould.  However, putting powdered kiln wash and smoothing it with a piece of glass or plaster’s float can give a less grainy finish.  If applied wet, the dried kiln wash can be gently sanded to give a very smooth surface.

Other refractory boards such as calcium silicate or vermiculite do need kiln wash to separate the glass from the mould.

Any refractory mould which has been hardened with colloidal silica will need to be coated with kiln wash to keep the glass from sticking.  The kiln wash needs to be re-applied each time the mould is used above tack fusing temperatures.  Otherwise it does not need renewal until or unless the kiln wash is chipped, scratched or in other ways damaged. 

Another popular separator is boron nitride.  It is sold under various brand names.  This must be applied each time the mould is used.

Texture Moulds

Texture moulds are popular but expensive and with limited designs. You can make your own unique ones with only a few items of equipment. 

An example made by someone else

Clay

Various forms of clay can be used. Roll out a flat piece using boards of 8-10mm thick to support the rolling pin and give consistent thickness to the clay. The board underneath should be covered in paper or cloth to make an easy release. I have found that grease-proof paper as used in baking works very well.  It releases easily from the clay.  

Paper clay provides light weight moulds that do not hold a lot of heat, but any standard clay will do the job. There are two approaches to developing the pattern. You can stamp the pattern into the wet clay with any prepared design on a stamp or other textured material. The other is to dry the clay to leather hardness. You can then incise the pattern you desire directly into the clay. Fire to bisque temperatures, and sand to remove any rough areas or undercuts. Kiln washing the mould before use is essential.

Using a patterned roller to impress the design on the clay

Fibre board

Various fibre boards can be used. Ceramic fibre board, Kaiser Lee board, Vermiculite board, insulating ceiling tiles such as Armstrong, and calcium silicate boards can be incised and marked as desired. The advantage to the ceramic fibre, insulating ceiling tiles, and Kaiser Lee boards is that they allow air to pass through the material. Kaiser Lee board of these three provides the easiest surface for incising. Calcium silicate has no fibres, but requires a separator. Ceramic fibre and Armstrong ceiling tiles have fibres, requiring a bit more work to get a smooth surface. Armstrong tiles require a separator, but ceramic fibre boards do not unless you harden them for durability.

Fibre paper

Three millimetre fibre paper gives a easy material for cutting with craft knives or scissors to the design wanted. You can draw through an existing stencil or copy the design with carbon paper. It is not easy to produce designs with lots of detail.  It is quick, does not require separators, but is probably a single use material, unless you use mould hardener and then kiln wash, although it still will be delicate. For large projects, the paper should be fired first to ensure the combustion of the binders do not produce gasses to cause bubbles or fogging.

Loose Material

Sand, whiting, and kiln wash provide easy materials for one-off designs. You can quickly draw the design you want into the flat loose material with your fingers, or tools. You can also use found items to press into the loose material. Place the glass gently on top of the material and fire. If you use sand, you should dust it with kiln wash or aluminium hydrate to ensure the sand does not stick to the glass.

Unique Designs

All of these methods will provide unique designs which will distinguish your work from others.

Steel Pipe for Slumping

Steel pipe as opposed to stainless steel can be used for slumping. It will spall, so there will be a need to clean up the flakes of rust after firing. But since there is so much spalling, putting kiln wash or boron nitride is a waste of effort. Each firing will flake off any separator painted onto the metal. Cover the pipe with fibre paper instead - 0.5 mm at least.

You need to advance in temperature slowly as the pipe drains the heat from the glass where it rests. My practice is to advance the temperature at 100C/hr to 100C with a 20 minute soak, followed by 50% increases in rate to 250, and to 500 with 20 minute soaks before proceeding to the next segment. This probably is more cautious than necessary on all but the first segment.

Fiber Paper Safety

There are often concerns raised about safety relating to the dust from Thinfire, a trade marked product from Bullseye. These concerns also apply to the Spectrum product called Papyros. The main constituents of these are cellulose, aluminium hydroxide, fibre glass and organic binders. It therefore is mainly a nuisance dust and irritant. Greg Rawles, a certified industrial hygenist with a scientific and common sense approach, says that the toxicology of fibre glass is not yet determined. So the best idea is to wear a P95 respirator while dealing with the dust – mainly the cleaning phase of dealing with the shelf. He also recommends keeping the kiln closed during the burn-out phase of the binders, although others recommend venting to avoid anything settling on the glass during the burn-out.

Some people seem to have skin reactions to dust including that from Thinfire and Papyros and tend to wear gloves. If you are wearing rubber or latex gloves for extended periods, it may actually promote a reaction to the gloves rather than a primary reaction to the dusts of the paper. So checking on alergic reactions to the gloves is advisable in addition to the dust. 

If in fact, you are reacting to fibre paper dust, consider using kiln wash instead. If this is not practical or desirable there are several things you should do.

• Use gloves (for those with sensitive skin),
• wear long sleeved high necked shirts and pull the gloves over the ends of the sleeves to prevent dust getting to your skin,
• vacuum the kiln with HEPA filters,
• dampen the powder with water spray before brushing,
• take precautions against taking the dust home by changing in the studio and placing clothing in plastic bags to take to the wash.

Brown Ceramic Fibre Paper and Board

A frequent concern about fibre board and fibre paper that appears brown when peeking into the kiln is that something has gone wrong.

Ceramic fibre papers and boards have organic binders that have to burn out during the firing. What starts as white later turns brown as the binders are burning out – often the smell is like burning paper. As the binders burn away, the fibre paper or board returns to its original colour.

The amount of smell or smoke is dependent on the amount of ceramic fibre you have in the kiln. If you have a thick board, you should think of venting the room, as there will be a lot of smoke.

Also if you are firing a large piece of glass, you should think of firing the binders out of the ceramic fibre before placing the glass on top. If you do not, the binders may not fully burn out, leaving marks of the smoke fired into your glass.