We started by adding 500 grams of the G2926B Whiteware base clear to 250g of water and 100g of Laguna gum solution. It was possible to stir all the powder in without a mixer. There were a few lumps left but they broke down overnight (yielding about 550 ml at 1.58 specific gravity). For the black we added 30g more of Mason 6666 stain (6%) and for white 50g of zircopax (10%). This increased the specific gravity to 1.63, higher than pretty well any commercial brushing glaze (if needed, there is plenty of room to add water to thin it for better application properties). The black recipe costs about 1.37 cents/ml for us to make (compared to Amaco C-1 Obsidian @ 3.92 cents/ml to buy). But the situation gets even better: If we were to add enough water to bring the specific gravity down to the 1.4 of C-1 there would be far more than 550ml.
Hobbyists and increasing numbers of potters use commercial paint-on glazes. It's convenient, there are lots of visual effects. But there are also issues compared to making your own.
G2926B - Cone 6 Whiteware/Porcelain Transparent Base Glaze
A base transparent glaze recipe created by Tony Hansen for Plainsman Clays, it fires high gloss and ultra clear with low melt mobility.