Maxwell Posted March 13 Report Share Posted March 13 Hello, I am looking for advice regarding raku glazes that separate or fall off of a ceramic piece during firing. I have extensive experience with high fire stoneware in glaze and salt firings. My raku experience is limited to work I did 50 years ago with crackle glazes and primitive firing techniques. I make all of my own glazes and recently have experimented with raku glaze formulas published by Gary Ferguson and a Ceramic Arts Daily publication of 15 tried and true glaze recipes. Maybe someone out there is aware of these. Recipes containing bone ash, soda ash, borax and ferro frits do not brush on particularly well and then are separating from the bisque ware during firing. I have experimented with different clays, glaze thickness and clay additives without much success. When fired to temperature, the glaze remaining on the pieces is otherwise quite nice. I am anew subscriber and this is my first use of the forum. Any thoughts? Quote Link to comment Share on other sites More sharing options...
Min Posted March 16 Report Share Posted March 16 Hi and welcome to the forum. Link to the Ceramics Arts Daily Tried and True Raku Glazes here if anyone uses any of these recipes. Giving this thread a bump, hopefully someone will chime in. Quote Link to comment Share on other sites More sharing options...
neilestrick Posted March 17 Report Share Posted March 17 No glaze is going to brush well unless it contains a lot of Gerstley Borate or you add the necessary ingredients to make it brushable, namely CMC gum. Typically a gum solution is made with 2 tablespoons of CMC to 1 gallon of water, and the solution is used in place of 1/3-1/2 of the water in the glaze. Since your glaze(s) is already mixed, you don't want to use that solution because there will be way too much water. You could add the CMC directly to the glaze, but it's difficult to get it to mix in well doing it that way. So instead, make up some gum solution that's really thick like snot. Mix 2 tablespoons CMC and 1/4 tsp copper carbonate (preservative) with 1 quart of hot water, let it sit overnight, then blend with a stick blender. If you're using small containers of glaze like pints or quarts, add a spoonful of the snot to the glaze and blend. See how it brushes, and add another spoonful if needed. Quote Link to comment Share on other sites More sharing options...
Maxwell Posted March 17 Author Report Share Posted March 17 Hey Neilestrick, Thanks for the gum info and technique. I have some gum and will give it the next test. Easy since I'm doing small test batches. I did use all of these glazes both dipped and sprayed, but could not get them to stick to the bisque ware during firing. The glaze literally peels half way off at about 800-1,000 F. Do you or anyone have a similar experience or work around that is effective. I've tested the addition of bentonite, ball clay and kaolin without any success. Thanks Again Quote Link to comment Share on other sites More sharing options...
davidh4976 Posted March 18 Report Share Posted March 18 I think the "Ceramic Arts Daily publication of 15 tried and true glaze recipes" are all cone 6 recipes and would not be well suited for Raku. I don't know about the Gary Ferguson recipes. Can you share your recipes here and we can take a look at them? Since the flaking is happening with both dipped and brushed, it makes me suspect the amount of clay in the recipe. With too much clay, the glaze can shrink during drying, crack, and flake off before firing. Quote Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 18 Report Share Posted March 18 (edited) 47 minutes ago, davidh4976 said: I think the "Ceramic Arts Daily publication of 15 tried and true glaze recipes" are all cone 6 recipes Lots of boron in those recipes Min linked. They look low fire / raku.. tried fergusona white, and two of the copper. Results were fine as I recall. Edited March 18 by Bill Kielb Quote Link to comment Share on other sites More sharing options...
PeterH Posted March 18 Report Share Posted March 18 7 hours ago, davidh4976 said: I think the "Ceramic Arts Daily publication of 15 tried and true glaze recipes" are all cone 6 recipes Just for the record Ceramic Arts Daily publish "15 tried and true glaze recipes" for (at least) raku, cone 6 & cone 10. https://ceramicartsnetwork.org/docs/default-source/uploadedfiles/wp-content/uploads/2015/08/15rakuglazes.pdf https://ceramicartsnetwork.org/freebies/guide/15-tried-and-true-cone-6-glaze-recipes https://ceramicartsnetwork.org/freebies/guide/15-tried-and-true-cone-10-glaze-recipes Quote Link to comment Share on other sites More sharing options...
davidh4976 Posted March 18 Report Share Posted March 18 3 hours ago, PeterH said: Just for the record Ceramic Arts Daily publish "15 tried and true glaze recipes" for (at least) raku, cone 6 & cone 10. Ah! I missed that there are three different versions of their "15" recipes! All of the raku recipes have less than 20% clay, so extra clay is probably not the problem. Quote Link to comment Share on other sites More sharing options...
justme Posted March 18 Report Share Posted March 18 (edited) Are you using the recipes with Gerstley Borate? Edited March 18 by justme Quote Link to comment Share on other sites More sharing options...
Maxwell Posted March 18 Author Report Share Posted March 18 (edited) Hello and thanks folks for getting involved. I am new to Ceramics Monthly and am not aware of all previous publications, so I am adding additional info to clarify the topic. I am talking about western Raku and I realize you all know the temp range (1470-1830F Cone 06 range) and that Cone 6 is 2232F which is stoneware high fire and my historical wheel house. I am sharing copies of the lead pages from the Ceramics Monthly regarding 15 tried and true raku glazes and the lead page from Gary Fergusons 3 part freebie series on raku glaze formulas. There are 2 photos of glaze tests I did(I usually use small pots as I want to see the effects on shape. All were fired to cone 06 and all fluxed nicely when the residual glaze settled back on the pots. The single pot photo hopefully shows the irregularity on the surface where glaze has fallen off before completion of the firing. These were all cone 06 or less glazes. In fact, the crackles which worked well matured as low as cone 010. My difficulty is really with trying to get the glaze to adhere during the temperature rise. Problem ingredients seem to be frits, borax, soda ash and bone ash. I tried adding different clays to the formulas without suggest, but never more than 5%. Maybe the solution is just adding more clay to the formulas, but why not state this in the formula from the get go. Anyhow, take a look and see what you think. Thanks!! Raku pdf version 3.pdf Edited March 18 by Maxwell Quote Link to comment Share on other sites More sharing options...
Babs Posted March 18 Report Share Posted March 18 Would the clay you are using be unsuitable for these raku glazes? Havent lookwd at your images If pots. Could be "Absolutely naked raku " technique:-))) Quote Link to comment Share on other sites More sharing options...
davidh4976 Posted March 19 Report Share Posted March 19 Is the glaze coming off during the firing and landing on the kiln shelf? If that is the case, it can be due to the way the wet glaze dries and cracks and falls off. If the glaze is not falling off onto the shelves, but is leaving bare spots, that can be a different cause. I can't tell which is happening from the description or photos. Min 1 Quote Link to comment Share on other sites More sharing options...
PeterH Posted March 19 Report Share Posted March 19 I hope that CMC has solved your problems, if not: - what cone/temperature do you bisque at - how dry is the glaze before you fire - what bodies have you tried (raku, e/w, s/w, hi-fire s/w, etc) - do you use real Gerstley B or a modern substitute Quote Link to comment Share on other sites More sharing options...
Maxwell Posted March 20 Author Report Share Posted March 20 Hey Folks, I'll add a bit more info. I have used several clays including a stoneware white, Salt body and Laguna's Raku K. The salt body I mix myself and the other 2 purchased. Glazes were sprayed, dipped and brushed. Dried overnight before test firing. Bisque to cone 06 which seems quite porous. I use what I think is real Gerstley B from Continental Clay in Denver. The glazes formulas I attached start separating off at about 800F and some does fall to the shelf guard. These little 2# round pots then look like a paper wasp nest, but with large cracks running throughout. 80-90 % of the glaze will sit back down, flux and adhere with a mature appearance at cone 06, but with lumps and thin shallow areas. At this point, I will probably continue to dip or spray, dry well and try approaching the glaze formulas as the problem. It seems that the borax, bone ash and soda ash are somehow involved and not adhering well. Adding more clay will likely be my next step. Tx PeterH 1 Quote Link to comment Share on other sites More sharing options...
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