AOEYnes Posted March 20, 2022 Report Share Posted March 20, 2022 I have a base glaze that I want to use. I first made this of only two parts clay and one part calcium borate, that worked ok for some time, but after a while it started crawling. Leaving large patches unglazed on the surface. This I worked around using kali feldspar. This caused the glaze to run, the glaze layer was way to thin, it pooled in the bottom. I added 5 % alumina hoping this would thicken the glaze, strangely it did not seem to affect the runny glaze in any way. I have not tested it extensively, but the single test showed runnyness and small bubbles in the glaze. I had bought some more AlO2, which I planned to add to my base glaze, but the 5 % addition did not show any of the wanted effects. When I now write this, a probable solution reveals itself, I will add some more clay, I think it will, if not solve it completely it will help alot. But the question remains, should I in this or similar cases add more AlO2, until it reaches the wanted consistency and stops running. The aspect of overfiring is probably worth considering, but we fire all stoneware and porcelain to 1260 C° and earthenware to 1040 C° and I try to make glazes that fit that range. Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 20, 2022 Report Share Posted March 20, 2022 It’s really hard to make durable glazes the way your are attempting. The variation in clay may be an issue, the solubility and ability to mix and distribute alumina are among some of the reasons predictability and durability along with repeatability will likely be an issue when making them this way. Have you looked at various published glaze recipes and is it possible to source the materials for them? Have you looked through something like Glazy.org? Just trying to get a sense of your overall glaze experience here. just to mention, your clay should contain silica, alumina and fluxes, likely melting around cone 10’ish. Boron lowers this melting point a bunch, so less boron or more clay to boron ratio likely makes this stiffer so to speak. Reducing boron will raise the melting point. In general when the melting point is too low, the glaze melts and gravity makes it run down and off the pots. Link to comment Share on other sites More sharing options...
Min Posted March 20, 2022 Report Share Posted March 20, 2022 Potters have been making glazes long before glaze calculation helped us along. It's going to take testing but I think this is totally doable. Really good article linked below on developing glazes, includes a few different methods for doing so. I would suggest making small bowl shaped test pots and try the glazes on the inside of them only. When I am modifying an existing glaze I like to use a triaxial blend, there on directions on how to do this in the link if you need it. Glazes for the Self Reliant Potter link here. http://www.nzdl.org/cgi-bin/library?e=d-00000-00---off-0hdl--00-0----0-10-0---0---0direct-10---4-------0-0l--11-en-50---20-home---00-0-1-00-0-0-11-1-0utfZz-8-00&cl=CL1.7&d=HASHb8171ab02a10e3ab23250b.13>=1 edit: "...but we fire all stoneware and porcelain to 1260 C° and earthenware to 1040 C° and I try to make glazes that fit that range." Just to clarify, you use different glazes for high and lowfire? Like Bill said less or zero boron needed for highfire but necessary for lowfire (for unleaded glazes). Link to comment Share on other sites More sharing options...
AOEYnes Posted March 20, 2022 Author Report Share Posted March 20, 2022 Ok, good answers. Thank you both. I use marine clay, we call it blue clay, it is very fine particled and contains oxides of many light metals, including aluminium and silica. I will try to lower the amounts of frits by adding more of this clay and see if that helps, before I go to the step of adding synthetic alumina. Link to comment Share on other sites More sharing options...
Piedmont Pottery Posted March 25, 2022 Report Share Posted March 25, 2022 On 3/20/2022 at 2:06 PM, Min said: Potters have been making glazes long before glaze calculation helped us along. Very true, but potters have also been making poor-fitting, non-foodsafe, nondurable glazes for a long time too. Not that the availability of of modern software has eliminated those problems. I started making glazes forty-five years ago using limit formulae and a slide rule, but I wouldn't do without my computer software now. Just because we can do something in a historical way doesn't really mean we should. If a potter has enough computer skills to post on an online forum, they have enough skills to use something like Glazy or Insight-Live. It can really help to progress the development of good quality glazes. Link to comment Share on other sites More sharing options...
Min Posted March 25, 2022 Report Share Posted March 25, 2022 1 hour ago, Piedmont Pottery said: If a potter has enough computer skills to post on an online forum, they have enough skills to use something like Glazy or Insight-Live. It can really help to progress the development of good quality glazes. Couldn’t agree more with the benefits of using a glaze calculation program. Re the OP in this thread, I read their post as using a local Norwegian blue clay as part of the glaze recipe. I did a quick search to try and find a general analysis for that type of clay but came up empty. If the OP has had an analysis done (and has a large supply of the same clay) then yes I would use glaze calc to come up with test recipes. Like you said there are a LOT of lousy recipes out there, including on Glazy. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.