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Underglaze exploration with Chris Scamehorn

I started the development of a white underglaze and a black underglaze for the studio. The reason behind this is due to the amount of material used in the studio and the cost of the underglaze. I looked up the 1 gallon retail cost of these items.
1 gallon of White underglaze = $130.00
1 gallon of Black underglaze = $140.00

In cases like this when I’m formulating, I like to have a starting point. I searched on the internet and found a link to a Ceramic Arts Daily article on the topic of making underglazes. Here is the link: http://ceramicartsdaily.org/ceramic-supplies/underglaze-ceramic-supplies-2/how-to-make-homemade-underglazes/
A common recipe for an underglaze will consist of 1/3 frit, 1/3 clay, 1/3 stain and a gum.  It did not take long to arrive at a nice looking black underglaze. I used Alberta slip as part of the clay in the recipe due to its iron content. Black underglaze Recipe:

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Black underglaze (1 coat)

Frit 3110                       50 g
Tile 6 clay                      25 g
Alberta slip                   25 g
Mason stain 6600       50 g
Macaloid                     .85 g
CMC gum                    .85 g

For the white underglaze, I started with tile 6 clay because it’s very white. EPK is a bit creamy looking and does contain more iron than Tile 6 or Grolleg. I used quite a bit of an opacifier to start, however the results came back yielding a creamy buff color. There was also a bit of a mud crack effect post firing. I tried a test with 10% titanium dioxide and the result was a beautiful light creamy yellow, but no white. Tin oxide is what got me to a very white looking underglaze. I decided to start with the whitest clay body in the studio as a base, Coleman Porcelain. So I used equal parts Frit 3110 and moist form Coleman Porcelain. This result was a beautiful opaque white glaze, but not underglaze. I had to raise the melting point so Alumina Hydrate was the next test. 12.5% was getting there, but it was still fluxing. 20% looked very good. I finally found a test that was desirable. At high temp the result was a beautiful opaque Shino looking glaze.

One of the desirable qualities about an underglaze is how it brushes onto the surface of bone dry greenware and/or bisque-ware. Gums are added to create this quality. I used 1% cmc gum and 1% Macaloid (Vee gum T). One issue I had was when I mixed up multiple small batches, the overall mixture was taking too long to dry on the bisque ware. I wanted to reduce the amount of gum overall, so I calculated out how many batches I made, then added in a batch without gum in it. I reduced the gums from 1% down to .85%. This result was great. The underglaze brushed on very nicely. It also worked well with a clear glaze over it. Since then, I have done more tests and they have turned out great. The following is the recipe:

In a blender mix:
Coleman Porcelain         50 g
Frit 3110                           50 g
Alumina Hydrate            20 g
Zircopax                           10 g
Tin Oxide                         10 g
Vee Gum                         .85 g
CMC Gum                       .85 g

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White underglaze (1-3 coats)

 

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White underglaze 1-3 coats (Duncan clear over)

 

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White Underglaze at cone 10-11 reduction (2 coats/ 1 coat)

Click link below to download article.

underglaze-exploration-with-chris-scamehorn

3 comments

  1. Pam Schick says:

    Hi chris! this experiment has been really interesting to follow. I tried your white ug and it worked great. then I tried your white ug with varying mixtures of the black ug to get various greys. they look great too, and are very dry. this week I am putting a Matt glaze over them to see what I get for a finish. I’ll let you know the result. thanks for all your experiments and knowledge. I think these might be useful for both high and low firings.

  2. Dixie Noble, Ph,D. says:

    Chris, it was a pleasure to have an independent study with you several months ago. I learned so much. Thank you. Potters have come a long way from digging the mud, making ware on crude wheels or in skillful hands. You have added the scientific knowledge and extreme patience required to achieve these marvelous results in end firing. How generous you are with us potters now and in the future. We look forward to experiencing even more of your earned knowledge.

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