Mastering Cone 6 Glazes Success

[DBPottery]

I’ve been working on developing my own cone 6 glazes over the past 18 months out of my frustration dealing with commercial glazes that didn’t behave well or contained ingredients that are suggested not to use for food safe glazes. Between using the Mastering Cone 6 Glazes book, a book by John Britt for help on colorants, and glazy.org for colors I made great progress. 

After a couple hundred tests to get the colors I wanted, I moved forward with testing on about 10 colors, including having them leach tested at a lab. 

I found it’s imperative to use glaze calculation software so material changes can be incorporated to keep the chemical properties the same over time in the base glaze and as materials might no longer be available. I used GlazeMaster, but need to start searching for another program that it actively updated and supported. It was a challenge to get a material analysis for each material. Many suppliers came back with no response. HighWater has able to provide something, while not all were as current as I would have liked, it was the best I could get. In cases where I was able to buy the whole bag of a material I reached out to the manufacture and found most just supply a “typical analysis” not an actual analysis for each production run. So, I ran with what I could get my hands on. 

I stayed within all the recommended colorant limits and the leaching test results all came back in a good range. I do want to point out I found for my materials analysis I received, many of the colorants contain impurities of less than desirable elements you don’t want to add in a food safe glaze. For example, a lead impurity is in most of the colorants. However, the leach testing was not able to pick up a significant amount, so it probably isn’t worth the expense to test for. One of the authors from Mastering Cone 6 Glazes mentioned since they have written the book, lab testing tools have greatly improved, which is probably why impurities of lead etc. was not detected at the time. 

I found all but the dishwasher test recommended by the Mastering Cone 6 Glaze authors to be a good test. Their dishwasher test failed everything, even glazes they said in their book are durable, so I just ruled that out as a good test. I started a topic on this a couple months ago and it was suggested to look at the stull chart and that resulted in the glaze looking to be a good glaze.

Now I am full scale and have made 5 gallons of each glaze. It’s going well for the most part, I’m just working on glaze thickness and a few more color options. I’m playing with double dipping vs dip longer. The dip longer appears to be the winner, but I will have to final answer once the pots come out of the kiln. The double dip seems to make the glaze really thick and there is little pin holes in the raw glazes that need rubbed down. 

I just wanted to share my experience and point out a few items that might be helpful to others.

Regards,

Dan

[Hulk]

Thanks Dan!

I also use GlazeMaster. Tony Hansen's Digitalfire may be the best option in terms of current support, updates, widespread use, etc.

If you haven't seen Tony Hansen's website, check it out - a true wealth of information there! His take on adjusting glaze specific gravity and thixotropy, so helpful!

https://digitalfire.com/4sight/library/thixotropy_and_how_to_gel_a_ceramic_glaze_73.html

I'm seeing much less pinholing than previous, am blowing off each bisque piece with compressed air and wiping with a damp sponge as well.

With you on double dip for outside of forms; a single fill and pour out is working well for the inside...

[liambesaw]

Insight live is what I use for glaze calc.  I like it, it's constantly updated and I can bring up a mix ticket on my phone while I'm out in the studio since it's all online.

Congrats on taking the plunge into glaze mixing, it's not for everyone but it definitely allows for more control over your product.

[neilestrick]

When I worked as a tech at a clay/glaze supplier, I was in charge of all the safety labeling for all the clay and glazes we produced. In addition to all the tests we had to have done on the products, we had to send several of our raw materials in to be tested for lead. I remember specifically that copper had to be tested, but I know there were a few others, too, probably cobalt and the other metals.

[DBPottery]

6 hours ago, Hulk said:

Thanks Dan!

I also use GlazeMaster. Tony Hansen's Digitalfire may be the best option in terms of current support, updates, widespread use, etc.

If you haven't seen Tony Hansen's website, check it out - a true wealth of information there! His take on adjusting glaze specific gravity and thixotropy, so helpful!

https://digitalfire.com/4sight/library/thixotropy_and_how_to_gel_a_ceramic_glaze_73.html

I'm seeing much less pinholing than previous, am blowing off each bisque piece with compressed air and wiping with a damp sponge as well.

With you on double dip for outside of forms; a single fill and pour out is working well for the inside...

I used Tony's website as well. Thanks for the link. That is interesting. All my experience with commercial glazes helped me get the right viscosity down. I have found at a certain thickness any drips become hidden, but not all glazes are as forgiving. 

I've always wiped down the bisque to get off duct, but haven't heard of the compressor trick. Don't give me a reason to go buy another toy... 

[Hulk]

Hey DB, you need a compressor, believe it! ...so handy for airing up tires, blowing out bike chains after cleaning, running impact wrench and other air tools, and,  uhm, blowing off pottery. I do a bit of bisque sanding, hence some air is very helpful for blowing off the work, my clothes, etc. before heading back inside (and hanging up the respirator).

Agreed that some glazes level off better than others, also one can go too thin (as well as too thick) with glaze application.

My take on Tony Hansen's thixotropy tips, a) one can have a wetter (lower specific gravity) glaze, hence thinner coating and wets the pots better, whilst b) the propensity to gel up more quickly helps control the dripping (better than a drier - or higher specific gravity- glaze that's not gelling well does). Wetting the pots better may help the pin holing as well.