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URL: 15 Tried and True Cone 6 Glaze Recipes

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Tried and True recipes. Really?

Books and web pages with flashy pictures are the centrepiece of an addiction-ecosystem to recipes that often just don't work. Maybe these are "tried" by a lot of people. But are they "true"? Most are so-called "reactive glazes", outside normal practice - to produce visual interest they run, variegate, crystallize, pool, break, tint, go metallic, etc. But this happens at a cost. And inside special procedures and firing schedules that need explaining. It is not obvious these are understood by the recipe authors or sharers. And these recipes are dated and contain troublesome and unavailable materials. We use frits now to source boron. Stains are superior to raw colorants, even in glazes like this. Many of these will craze badly. And many will not suspend in the bucket. And will run during firing. Reactive glazes have other common issues: Blistering, leaching, cutlery marking, fuming. Trying colors in differing amounts in different base recipes is a good idea. But the project is most beneficial when it shows color response in terms of quality recipes of contrasting chemistries. The point of all of this: Understand a few glazes and develop them, rather than throwing spaghetti against the wall hoping something sticks. Commercial reactive glazes are an alternative also.

What has the trust in online recipes come to?

These tests of a recipe called "Strontium Crystal Magic". The potter tried it on different bodies and firings. But instead of producing the magic crystals like the pictures, the surfaces fired totally matte. Reasoning "why would anyone put a recipe on line that does not work", she blamed one of the materials. Others fed that with rumours of claimed issues in its consistency. Admittedly, this glaze is meant for layering over others - but the source did not say that. This underscores misguided trust in trafficked recipes that most often lack sufficient documentation. Crystal glazes, by necessity, need to have a high melt fluidity. The crystals develop best with a specific cooling curve having a controlled fall at a narrow temperature range. Cool faster, they don't grow, slower and they matte the entire surface. Other factors, like clay body and glaze thickness are involved. People who post glaze recipes like this often do not document them well because they do not fully understand their mechanisms.

Is the N505 cone 6 matte glaze recipe what you think it is?

This recipe is from page 2 of the booklet: "15 Tried & True Cone 6 Glaze Recipes". Click the following code, G3955, to see more information on how we compare it with G2934 and another matte, G1214Z1. This flow test and these test tiles were in the same kiln, fired at cone 6 using our PLC6DS schedule. Obviously, the defining characteristic of N505 is its extreme melt fluidity, clearly it is not a native cone 6 glaze (it's a lower temperature one being used above its range). Still, the surface on the N505 tile is arguably more interesting, that's why it's popular with potters. But is it functional? Some felt pen marking helps reveal one big difference: The micro surface of the G2934 is much smoother. From the chemistry shown on Insight-Live side-by-side screenshot very low Al₂O₃ and SiO₂ are evident. This also reveals it should fire glossy, so it is a "crowbar matte", forced to be such by 6% addition of magnesium carbonate. I was understandably suspicious that this glaze would have more issues than it actually does. Although the surface is rough and it does mark and stain, it can be cleaned with effort. The low SiO₂ suggests it would cutlery mark but it does seem quite hard. However on the matter of leaching the jury is still out (a stain needs to be added for testing in an acid). Crazing is another possible issue. Our G3924 recipe, although more boring, excels on all four of these tests.

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