Spodumene F&S

Crazing, a web of fine cracks, forms when a glaze shrinks more than the clay as they cool. Lithium makes a glaze shrink much less than sodium or potassium do. Swap some of the glaze's feldspar for spodumene, starting with 5 grams per 100 grams of dry glaze, then test and adjust.

It can. Lithium changes how some colorants develop, so fire test tiles of your colored glazes after you add it.

Both bring lithium, which helps a glaze melt and makes it shrink less as it cools, to cut crazing. Spodumene has more lithium. Petalite has less lithium and more silica, and it's the usual choice for heat-resistant clay bodies. To use petalite in place of spodumene, start with about 1.6 times as much and take out some silica. Test either way.

Yes. Too much can make the glaze shrink less than the clay as they cool. The glaze gets squeezed and can flake off rims and edges, sometimes in sharp chips. This is known as shivering. If you see it, use less spodumene or petalite.

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.