Brand : REFSAN
Price : 11,71TL


Colemanite has been a popular natural source of insoluble boron for many decades. It is similar to Ulexite in its oxide contribution to glazes (although the latter sources Na2O also). Frits are used as boron sources in industry whereas potters and smaller companies have used colemanite.

Colemanite does not melt as low or as uniformly as Ulexite. Gerstley Borate contains significant amounts of colemanite. Pure colemanite, however, is much higher in B2O3 than Gerstley Borate.

Higher percentages of colemanite in a glaze can result in wrinkling of the fired surface, likely due to to a phenomenon called 'decrepitation' (very active decomposition) that occurs when colemanite is heated. The glaze layer can actually delayer, even disintegrate if sufficient colemanite is present (pieces of glaze can be spit off the ware onto other ware or the kiln shelf. For many applications Ulexite is thus a better choice. If you must use Colemanite, be sure to screen out any materials coarser than 200 mesh, or ball mill the glaze. Gum or other binders also help.

Colemanite is available from Turkey, Chile and California. The chemistry of these varies quite a bit, and of course, none of the available materials have the theoretical chemistry shown here.