Wollastonite W-20 (325 Mesh)

They're the same mineral at different grain sizes. W-20 (325 mesh) is our all-purpose glaze grade and the best pick when a recipe just says "wollastonite." W-30 (400 mesh) is the finest, for smooth, thin coats. W-10 (200 mesh) and Nyad-G, with its long, needle-shaped crystals, are mainly for clay bodies. Mesh counts the openings per inch in a screen; higher is finer.

Not gram for gram, because wollastonite brings silica along with its calcium. To replace 10 grams of whiting, use about 11.6 grams of wollastonite and take 6 grams of silica out of the recipe. Then fire a test tile. The swap is worth trying when a whiting glaze pinholes, because wollastonite gives off no gas in the kiln.

Glaze and clay recipes go by weight, not by volume, and they don't count water. Each ingredient is a share of the dry total. 2% means 2 grams for every 100 grams of dry ingredients. For a 500-gram batch, that's 10 grams. Colors and opacifiers are often listed as extras on top of a recipe that adds up to 100, written like "+2" or "add 2%." Weigh those the same way: 2 grams for every 100 grams of the base recipe. A digital scale that reads to 0.1 gram makes small amounts easy.

A test tile is a small piece of the clay you use, glazed and fired just like your real work. Raw materials vary from bag to bag, and results also change with your clay, how thick you apply the glaze and how your kiln fires. A test tile is the only way to know what you'll get before you glaze a whole batch of pots. Write what's on each tile on the back (an underglaze pencil works), and keep notes so you can repeat what works.

Yes, whenever you handle the dry powder. Fine dust is the main hazard with most raw materials, and some can harm your lungs over time. Wear a NIOSH-approved respirator (N95 or better) while you weigh and mix. A basic dust mask that isn't N95-rated won't protect you. Once a material is mixed with water, dust is much less of a problem, but wipe up spills with a wet sponge before they dry, and mop instead of sweeping. Don't eat or drink while you work, and wash your hands afterward. Check each product's Safety section for anything extra that material needs.