[Clayart] Zinc and Mimi - RR

William R Schran wschran at twc.com
Tue Sep 7 21:04:08 UTC 2021

I buy calcined zinc. Democrats brand from US Pigment Corp. If I calcined my own I would fire in bisque bowl only to about 1300F. Firing hotter will make it clump up and need to be ground.

Sent from my iPhone

> On Sep 7, 2021, at 1:38 PM, David Lyons <lyonsd at plbb.us> wrote:
> Hi Bill, Would you share your process in how to calcine Zinc?  
> Dave Lyons
> Sent from my iPhone
>> On Sep 7, 2021, at 6:47 AM, sumi <sumi at herwheel.com> wrote:
>> Bill
>> Thanks, that is helpful. I am about to mix a batch of crawling glaze which requires CMC to hold it on; too little CMC and it cracks and falls right off, too much and it doesn't crawl. This gives me some kind of ball park to aim at. I'll try mixing some CMC solution in with the dry ingredients, instead of just adding it after I've mixed and screened the glaze.
>> Sumi
>>> Not dumb at all!
>>> I first explored crystalline glazes back in the 1970's when there was
>>> not much current information in libraries. Had a horrible time getting
>>> a thick application of glaze not to crack and peel. Tried couple ways
>>> and ran across information about adding gum binder to glazes...
>>> I mix CMC with hot water using a tableware serving spoon that I guess
>>> is about a tablespoon + a teaspoon to plastic mayo jars (30 oz size)
>>> containing hot water. Give a shake up then let sit to wet all the dry
>>> CMC for a couple days.
>>> With my crystalline glazes I add approx. 1/4 cup CMC solution to
>>> 100-200 grams dry glaze, stir and sieve and add water as needed to get
>>> brushable consistency.
>>> Bill
>>>   -----------------------------------------From: "sumi"
>>> To: clayart at lists.clayartworld.com
>>> Cc:
>>> Sent: Monday September 6 2021 7:40:39PM
>>> Subject: Re: [Clayart] Zinc and Mimi - RR
>>> Bill,
>>> How do you initially wet the dry glaze with CMC solution? I have CMC
>>> solution which I made by mixing CMC into hot water; but do you add a
>>> few
>>> spoonfuls of this to a couple of quarts of water and mix it into your
>>> dry glaze to create a thick slurry? And then add more water? Sorry,
>>> when
>>> I write it down it sounds like a dumb question.
>>> Sumi
>>>> Ron,
>>>> Having worked with crystalline glazes rather extensively where the
>>>> glaze contains about 25% zinc I do two things to help with dry
>>>> shrinkage of the glaze on the pot that can cause cracking on the
>>>> surface and crawling. First, I only use calcined zinc oxide.
>>> Second, I
>>>> initially wet the dry glaze with a gum solution, usually CMC and
>>> then
>>>> add water to achieve proper consistency. The gum solution helps to
>>>> prevent the crystalline glaze, that contains little or no clay, to
>>>> bind to the pot and prevent cracking/peeling as the glaze dries and
>>>> shrinks.
>>>> Bill
>>>> William Schranwschran at twc.com703-505-1617
>>>> -----------------------------------------From: ronroy at ca.inter.net
>>>> To: "Clayart international pottery discussion forum"
>>>> Cc:
>>>> Sent: Sunday September 5 2021 1:46:55PM
>>>> Subject: [Clayart] Zinc and Mimi - RR
>>>> I have two questions!
>>>> Does anyone have a copy of Mimi Obstler's book "Out of the Earth
>>> Into
>>>> the Fire" that they would like to sell. I have a customer for you.
>>>> Has anyone had the unfortunate problem with a glaze fluxed with
>>> zinc
>>>> oxide - where the glaze starts to crawl after being in the bucket
>>> for
>>>> a while? Apparently zinc oxide re-hydrates and shrinks excessively
>>>> causing crawling problems.
>>>> Has anyone had the problem and found a solution?
>>>> OK - that's three questions
>>>> Thanks for any enlight enment!
>>>> RR
>>>> Ron Roy
>>>> ronroy at ca.inter.net
>>>> Web page ronroy.net
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