Boron nitride is a synthetic material that's available in several forms, including powder, solid, liquid, and aerosol spray. Most types of glass will not stick to boron nitride; as a result, the liquid and aerosol forms can be used in kiln-forming as a release on slumping molds.
Although boron nitride is much more expensive than kiln wash, it does have several advantages. Applied correctly, it is smoother than kiln wash. It's also less dusty, and may be less likely to mark the slumped glass than kiln wash. It can be used on both stainless steel and clay molds, but most formulations of boron nitride are not suitable for use on the kiln shelf.
Depending on the quality and purity, liquid boron nitride may be used as is or diluted with distilled water. It works best when diluted to the consistency of whole milk. Boron nitride aerosol sprays can be used straight out of the can, and no mixing or diluting is necessary.
In general, boron nitride is rated for kiln use only to around 1550F/840C. Some varieties of the product will claim higher rated temperatures, but usually this refers to the product's use in a reducing atmosphere, rather than in the oxidizing atmosphere typical of most kilns.
Tomorrow's tip will contain specific information about using boron nitride on slumping molds.