Is there a best separator?

 Is there a best separator?

Kilnforming separators

Separators for kiln forming come in various forms. Chemicals, liquids, sprays, refractory fibre paper, kiln wash, and others I suppose. Which is best?  Each separator has its uses. No one is useful in all circumstances.  Some will be best for one circumstance and others for another.

Boron nitride

Boron nitride (BN) is a high temperature lubricant. It can be sprayed or brushed onto the mould. It adheres to smooth non-absorbent surfaces.  BN is among the most expensive of separators for glass. It seems most useful on detailed, texture and casting moulds. BN is often recommended for steel moulds as it adheres to it better than kiln wash.  Although kiln wash will work as a separator on steel, boron nitride is easier to apply.  Various conditions apply to its use. 

Kiln wash

Kiln wash works well on slightly absorbent surfaces – ceramic moulds, and shelves, for example. It is the least expensive form of separator.  It is shipped as a powder to which five parts water is added to one of the powder.  This makes a liquid that can be applied to any appropriate surface.  It can be sprayed or brushed. The mix can be with less water on very absorbent surfaces, showing some of its flexibility. 

Almost all kiln washes contain kaolin which helps keep the alumina hydrate in suspension.  But most importantly, allows the solution to be applied evenly.  However, the same kaolin also slowly changes to a crystalline substance by 900ºC/ 1650º that sticks to glass. It needs to be re-applied after every full fuse.

Refractory fibre paper

Shelf paper works well on flat surfaces and simple moulds.  It is a moderately priced separator.  Two of the popular trade names are Papyros and Thinfire.  They both contain alumina hydrate but with different binders.  They provide a smooth surface for the shelf and cylindrical shapes. They are not so good at separating glass from irregular surfaces and incised details.  The shelf paper disintegrates after firing. Although it can sometimes be used several times if undisturbed.  The resulting powder is an irritant and should be disposed of carefully.

There are thicker refractory fibre papers.  These normally range from 0.5mm to 6mm.  Thicker versions are called blanket.  These have the same characteristics as shelf papers, although coarser.  They also do not use binders to keep them together.  These are most useful in forming moulds and insulating glass from rapid temperature changes.

 

The general statement is that there is not one separator that is best in all circumstances.  Each has its strengths.  Knowledge of the objective of the firing and its conditions will help in choosing the right one.