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John255

Member Since 23 Feb 2013
Offline Last Active Jun 12 2014 09:07 PM
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Topics I've Started

The Calico Glazing Mystery

10 August 2013 - 06:39 PM

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In the late 70's I was out in Seattle and stumbled upon this lovely pot in a gallery. I was completely puzzeled by how the beautiful four glazes could have been applied in abstract pattern.  There are no overlaps.  I bought it for $20 and got the makers card that read "Charles Rothschild, Barlow Pottery, Sandy Oregon."

 

I wrote Charles a letter saying how much I admired the pot and asked about the glazes and how they were applied.  In a couple months I received a nice letter telling me about a take-off on Shaners Red, and the white being Rhodes basic #32 white, etc. all fired to cone 9 reduction, and not a word about how they were applied.  I wrote again and never had a reply. 

 

About once a year since then I take the pot in hand and try to figure out.  It's hard to believe each  pour would be waxed to protect from next pour?  The piece appears to be slab made which again would add to the time cost.   It does appear to be single-fired because the lid cut divides the glaze pattern as shown in photo 1.  Could this be an early laser cutting?  Photo 7. also shows a perfect cut- back which points to being done after glazing at leather-hard.

 

Anyway some of you old timers out there (not the Old Lady please!) may know the potter and/or the process, and would like to share your ideas.  Hope you find the puzzle interesting.

John255


Comparison Of Slow & Fast Cooled Iron Reds.

26 June 2013 - 07:47 PM

This thread is directed toward those ^6 potters who have an interest in Iron Red glazes but have manually controlled kilns that do not easily allow soaking and extended cooling.

The slow cooled samples were fired in a 1.5 cu.ft., computer controlled test kiln using Steven Hill's firing schedule for bisque ware. Essentially, this was slow up and down with a one hour hold when ^6 went over and another hour at 1600F. The fast cool firing was done by a friend in a 3.5 cu.ft. Jen-Kiln with 3" bricks, using only the Dawson sitter with no soaking, no pyrometer, and no extended cooling. Self-supporting witness cones were used in both firings.

The glaze formula was Bailey's Red: Custer 47%, EPK 4%, Bentonite 2%, Bone Ash 15%, Lithium Carb. 4%, Talc 17%, Silica 11%= 100%. Plus a short line blend of 12%, 15%, and 20% Spanish Red Iron Oxide (SRiO). All samples were dipped in the same glaze bucket.

Observations:


Photo one shows a greater red color difference between 12%, and 15% SRiO than the difference between slow and fast cooling. Although the slow 12.5 hour firing did promote slightly more red the 7.5 hour fast cooled samples had more textured pattern, and by my opinion were more desirable. This was especially true for the 15% sample where there was a lot of gold speckling. I'm not sure what this is, but I've heard it called "pyrite." My supplier list Spanish Red Iron Oxide as 80% FeO3. Although there are many variables in a test like this the one that seems most important is the quality and quantity of iron used.

Photo two shows larger samples of 3.5" high yunomi's, with same Bailey's glaze at 20%. The slow cooled was very smooth, more toward kaki color, and wonderful to the touch. Once again there was more pattern in the fast cooling. I'm also experimenting with Steven Hill's Strontium Crystal Magic glazes so will continue to fire my iron reds slow. Hope this post is handy for some of you who may have thought iron reds were not for you.

Regards,

John255
 


Steven Hill's Firing Schedule For Bisque?

13 May 2013 - 03:14 PM

Does anyone have Steven Hill's glaze firing schedule for bisque?
The schedule in his article is prolonged in the beginning because his work is single fired.
Thanks.
John255



Clear ^6 for Mason Stains

26 April 2013 - 02:48 PM

Someone may have tested the formula recommended by Mason and could supply some input. I could not get an email response from them so I called on the phone. They recommend the following transparent large cone 6 for most of their colors.

F-38 frit 32%

Kona F-4 Spar 26%

Silica 19%

Whiting 13%

EPK 10%

The formula looks quite old. F-38 is and odd frit by Fusion Co. that contains about 18% strontium carbonate. The closest Ferro frit is 3292, but it only has 4% strontium and other components of 3292 are not close. I personally don't think that amount of strontium is going to influence the colors very much.

For the other components of F-38 the Ferro frit 3124 is fairly close, but it does not contain strontium. When I get around to testing this formula, and to avoid finding F-38, I will use 3124 and test with and without about 10% added strontium carbonate to see if it indeed affects the colors significantly.

John255

Pot Decoration Trials On Computer

26 March 2013 - 12:26 PM

One day when I was feeling square I made a squarish mug.

Since this was a new shape I had no plan of what decoration, or how it was to be glazed.

So I thought about taking a photo of the bisque piece and discover experimental designs using a simple drawing app on the computer. Apps like Paint Brush for Mac, or Microsoft Paint that comes with Windows will do.

I will choose one of the designs for a prototype and use Mayco Coat & Stroke as underglaze on the #130 porcelain. Then glaze overall with John's clear, and fire to cone 6 . Previous test show this works well. See attached.

John255

Attached File  Mugs -Angle-s.jpg   132.03KB   118 downloads