oldlady Posted February 25, 2022 Report Share Posted February 25, 2022 there has been a lot of discussion of black clay and the difficulty of finding a good glaze fit. at least, that is what i have gotten from reading questions and answers on the forum for a few years. i have at least one block of that clay and want to find a good base glaze that i might color with mason stains. does anyone have it solved yet? thanks Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted February 25, 2022 Report Share Posted February 25, 2022 While there are a couple exceptions to the rule out there, some general things to mind regarding black clays, especially ones coloured with manganese or ochre: -your bisque fire is important! Black clays are more prone to pinholing than even red ones, and need lots of time to burn stuff off. Give it lots of time and lots of ventilation/circulation. Some black clays you can stack in the bisque, some don’t off gas properly if you do this. Hotter isn’t always better, but slower is. A bisque to cone 05 or 04 is usually a good start. It’ll prevent a lot of issues down the road. If you find your bisque isn’t as porous as you’d like it, you can flocculate your glazes a bit to compensate, or just go a little lower and give the bisque a soak. -The black clays will all “eat” a lot of coloured transparent glazes, meaning they just don’t show well. You need some opacifiers in your life. Some clays have some tiny amounts of chrome contamination, and can give tin a pink tinge. Not all of them, but some. If you don’t want that, stick with zircopax, and maybe some titanium. If you’re wanting to colour a base glaze with stains, definitely add some zircopax to make them be able to pop. 3% to start, but you’ll have to play with it. -rutile blues, especially ones with an Alberta slip or Ravenscrag base look FAR better on red and black clays than they do on white or buff. Variegated glazes get a fanatastic boost on these clays if you can keep them from pinholing. (See comment about bisque). -Many black clays don’t like going over cone 5, and can be very prone to bloating. Adjust your firing cycle accordingly. Many have had good results with a slower approach towards the end of the firing, and a short soak hold to make sure pinholes are minimized. \ Link to comment Share on other sites More sharing options...
oldlady Posted February 25, 2022 Author Report Share Posted February 25, 2022 thanks, callie. i knew there was something to be aware of and you have condensed several of the previous questions into an understandable answer. first thing i will check the standard website to see if there is any info re 266 properties. and call their tech person. Link to comment Share on other sites More sharing options...
Leaman Pottery Posted February 25, 2022 Report Share Posted February 25, 2022 Thanks from me too Callie! I have acquired some black and dark brown clay and want to use it. Love the pics on your links. The yarn bowl is awesome. Link to comment Share on other sites More sharing options...
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