Copper Oxide Red

Only in a reduction firing, where the kiln is short of oxygen (usually a gas kiln), or in raku. In an electric kiln it gives green, the same as any other copper. The red color of the powder doesn't carry into the fired glaze.

Start with a proven copper red recipe written for your firing temperature, and follow it closely. Copper reds use very little copper, often half a percent or less, usually with about 1% tin oxide. Glaze thickness, when the reduction starts and stops, and how fast the kiln cools all change the color. Fire test tiles in a few spots in your kiln, because the atmosphere varies from spot to spot.

Copper red is one of the hardest glazes to get right. Thin spots often fire clear, because some of the copper escapes as vapor. Too little reduction, or reduction that started late or ended early, can leave it gray or green. Very thick spots can turn dark and muddy. Apply an even, fairly thick coat, keep notes on each firing, and change one thing at a time.

Yes, with a conversion. Red copper oxide carries the most copper per gram. 1 gram of red copper oxide supplies about the same copper as 1.1 grams of black copper oxide or 1.55 grams of copper carbonate. Convert, then fire a test tile.

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.