Dialogue on Glaze Thickness

with Mike Oliver

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Zinc Silicate Crystalline Glaze Pottery

A chronicle of my recent progress and a way for me to keep it straight in my head!

From: Michael Oliver
Sent: Sunday, June 26, 2011 11:21 PM
To: pdh-at-zircarceramics.com
Subject: Glaze loading 

Phil,
I recently fired the urn pictured in the attachments.  The lid looks nice and had one barely wet coat.  The body has sparse and disappointingly small crystals for the hold time and I'm wondering if I got the glaze on too thick.  The glaze is a 3,3,3 blue black 3110 base and if my calculations are correct I probably have 1g. per cu. in. on the pot.  It's the first time I have ever tried calculating the glaze loading so I don't have any bench marks.  In looking at the numbers from your display that was made for Tampa it looks like I have too much glaze on the pots and it's inhibiting my crystal growth.  Does that sound right to you?
Mike

 

From: Phil Hamling [mailto:pdh-at-zircarceramics.com]
Sent: Monday, June 27, 2011 9:02 AM
To: Michael Oliver
Cc: _PDH @ home
Subject: FW: Glaze loading

 Mike,

This is exactly the type of thing that got me looking closely at glaze loading. I found similar things happening. I suggest you do a study of horizontal pieces with a range of glaze loadings and a firing schedule with ups and downs so you can determine at which point the crystals nucleate and how they grow at different loadings and temperatures.

Each glaze is truly different but I think you will get the sense that:

1) As thickness (or loading) increases the nucleation rate decreases.

2) Growth rate can have a bimodal relationship relative to thickness, meaning that at a "normal temperature" glazes will exhibit a given growth rate, but as you increase, or decrease, the thickness the rate will increase. I've also seen that some glazes exhibit much faster growth at very low loadings.

Keep in mind that the rate of temperature change can impact nucleation. Generally fast changes cause nucleation.

Phil

From: Michael Oliver [mailto:oliverpiano-at-yahoo.com]
Sent: Monday, June 27, 2011 11:50 AM
To: Phil Hamling
Subject: Re: FW: Glaze loading

Thanks Phil,
The pot in the pictures was to be an urn for a friend.  It turns out that at 340 cu. in. it's too small anyway and I will have to fire the second one that I made that will hold 460 bisqued.
I'm trying to make an educated guess without much education as to glaze adjustment for the body of the 2nd one.  I'm thinking of adding 1/2 g. zinc since I forgot I had been doing that  with this  base when I mixed the glaze from memory instead of notes and also lower the glaze loading to about 0.70 from 1.00g/sq.in. Does this sound like a reasonable plan to you?
Mike

 

From: Phil Hamling [mailto:pdh-at-zircarceramics.com]
Sent: Monday, June 27, 2011 12:33 PM
To: 'Michael Oliver'
Cc: _PDH @ home
Subject: RE: FW: Glaze loading

 Mike,

I'm glad to help.

Plan B sounds like too much of a butt pull for my liking. I'd hate to say yes or no and see it come out like poop. I've always been one to test, test then test some more so you have that 6 sigma confidence level before diving in head first.

But…..if a butt pull is in order…..I would guess more zinc would give you more crystals, as would putting it on thinner. Will it give you what you are looking for? Maybe. Maybe not. Hence the testing.

Phil

From: Michael Oliver [mailto:oliverpiano@yahoo.com]
Sent: Monday, June 27, 2011 2:41 PM
To: Phil Hamling
Subject: RE: FW: Glaze loading

Thanks Phil,
Actually everyone but me thought the one in the picture was beautiful, so I'll try plan B and since I have bad feelings about how the pot will do in the firing (thrown in two sections) and I have a few small pots to test with I'll also try just adding the zinc and just less glaze so if I have to throw another I should have some idea.
Remember even Spock had to make a guess one time on Star Treck.  He wasn't very comfortable with it though.
Mike

 

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Phil Hamling

376 County Route 1

Warwick, NY, USA 10990