From: Jon Dunlavy [j_dunlavy@yahoo.com]

Sent: Friday, May 18, 2012 5:00 PM

To: John Tilton; Ulrike Franck; Gordon Czop; Joerg Baumoeller; PHIL HAMLING

Subject: Re: Swimming out to the Ship

Hello everybody,

I would replied with some information earlier but I was in China for a while and yahoo.com was in Chinese with no way to convert it to English.

You all have made some great progress with the moly crystals.

I have noticed a few thing with regards to them in my work:

1. these glazes are very unpredictable, they can work well on the test tile and then fail on the pot.

2. re-firing (many times) with or without adding glaze to the fired/ failed pot sometimes can be the best thing that ever happened to that pot.

3. Molybdenum oxide seems to work the best (I don't think making powellite is necessary).

4. fast firings are sometimes better.

5. moly crystals are nothing like zinc and titanium crystals, they seem to form from the vapors that are next to the pot being redeposited when it is cooled, therefore a tighter kiln load seems to help them form (and can cause moly crystals on pots next to them).

6. titania seems to help get them started

A few notes on Moly triox (greenish/ whitish/ blueish) vs moly disulfide (black/ dark gray):

1. firing moly disulfide generates sulfur trioxide around 599F when it begins to melt/decompose and combine with oxygen (in an oxidizing environment) and become moly triox (moly triox melts at about 1463F)

2. you get the same amount of molybdenum from moly sulfide as you would from moly triox if you use 111.19% of moly disulfide

3. sulfur trioxide is highly corrosive and causes severe burns. when it escapes as vapor from the kiln it can re solidify (appearing as smoke). it is highly hygroscopic, combining with water in the air (or your lungs) and form sulfuric acid. (this is why I avoid moly disulfide).

I can share certain things but I have to be mindful of my work; I formulate and manufacture glazes professionally for Clay Planet/ Western Glazes and some of my knowledge is proprietary to the company, so some stuff must be discovered on your own.

I will help if I can.  

When I get a chance I will post some pics, I am prepping for a June 10th open studio event here in the SF Bay area so I have been busy.

Regards,

Jon Dunlavy

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From: John Tilton <john@tiltonpottery.com>
To: Ulrike Franck <ulrike.franck@email.de>; Jon Dunlavy <j_dunlavy@yahoo.com>; Gordon Czop <gczop@hvc.rr.com>; John Tilton <john@tiltonpottery.com>; Joerg Baumoeller <jbaumoeller@terra.es>; PHIL HAMLING <pdah@optonline.net>
Sent: Thursday, May 17, 2012 2:42 PM
Subject: Swimming out to the Ship

Hi Everyone,

I'm taking this afternoon to relearn Seger formulas, and to try to catch up with you.

A few comments.

1) I have a little 8 x 8 x 6 inch test kiln and I would be happy to run some tests if there is something that you would like to see, and do not have the time to do it. This would help me swim out to the ship, so to speak. I also have a little bit of time these days, which is not that normal.

2) I like the idea of making powellite and sheelite because I can do that outside, where the SO2 and SO3 fumes can escape more easily. Even though I'm not in the shop when the kiln is firing most of the firing, I think stuff like this hangs around, and builds up over time.

3) Here is a thought from someone who knows next to nothing about these crystals, I would think that the feathery crystals would be produced at a hotter temperature than the square ones. My reasoning is that when you have zinc crystals, if you try to hold at a too hot temperature, you get spikes and axe heads. As you lower the temperature of the hold, you get a round crystal. To me it appears that the fern like crystals correspond to the axe heads.

4) Am I correct in thinking that these moly crystals form in a totally different way than zinc or titanium crystals? Do we think that they are just deposited on the surface of the glaze by fuming. It is true that Ms. Bassett said that a tile with moly crystals would see them disappear in 3 seconds when dipped in hydrofluoric acid. I'm just trying to get a basic understanding here.

5) With respect to fuming, I think the ideal temperature is 700C to fume with tin chloride. This is the temperature that the salt glaze people used in the late 60's.

Thank you,

John