From sculpture to functional: It's like starting over

[BlueSky]

Hello Clay People:

I've been making large outdoor sculptures for 30 years. But when my expensive Heath bowls began to chip and crack, I thought, hey, I have clay. I have glaze. I have a kiln. Voila. I enjoyed making functional ware so much, I decided to keep on keeping on. But man o man, this glaze conundrum. I miss slapping whatever on my sculptures (mostly oxide washes) and not worrying if someone is gonna drink some heavy metals leaching into their coffee. 

I am following y'all and am overwhelmed by glazes recipes and crazing, etc.  I really like the idea of finding one good base clear glossy glaze and one good clear matte glaze. I have an extremely small studio (Bay Area, CA small). I don't have space for lots of chemicals. I don't want to spin my wheels chasing a bunch of recipes. No space + not a lot of patience + pea brain for chemistry = I just want to make my cups and put a safe glaze on them. Is that too much to ask??!!!

Finally the Question: Do you think I am going to have a better fit and durability, etc using glaze and clay from the same company, like Laguna? B-mix clay and Laguna MS29 Clear Bright Glaze  and MS67 Semi Clear Matte? I mean, I'm thinking, if I was Mrs. Laguna, I'd go ahead and test my glazes on my insanely popular clay called B-mix.

(I just purchased 10 lbs of each today, so obviously I am going to mix it and test it. Maybe I'll get lucky. )

[liambesaw]

2 hours ago, BlueSky said:

Hello Clay People:

I've been making large outdoor sculptures for 30 years. But when my expensive Heath bowls began to chip and crack, I thought, hey, I have clay. I have glaze. I have a kiln. Voila. I enjoyed making functional ware so much, I decided to keep on keeping on. But man o man, this glaze conundrum. I miss slapping whatever on my sculptures (mostly oxide washes) and not worrying if someone is gonna drink some heavy metals leaching into their coffee. 

I am following y'all and am overwhelmed by glazes recipes and crazing, etc.  I really like the idea of finding one good base clear glossy glaze and one good clear matte glaze. I have an extremely small studio (Bay Area, CA small). I don't have space for lots of chemicals. I don't want to spin my wheels chasing a bunch of recipes. No space + not a lot of patience + pea brain for chemistry = I just want to make my cups and put a safe glaze on them. Is that too much to ask??!!!

Finally the Question: Do you think I am going to have a better fit and durability, etc using glaze and clay from the same company, like Laguna? B-mix clay and Laguna MS29 Clear Bright Glaze  and MS67 Semi Clear Matte? I mean, I'm thinking, if I was Mrs. Laguna, I'd go ahead and test my glazes on my insanely popular clay called B-mix.

(I just purchased 10 lbs of each today, so obviously I am going to mix it and test it. Maybe I'll get lucky. )

Good call on ordering their glaze for a good fit.  Formulating a durable base glaze can be a sometimes frustrating process that takes some investment in time and money up front.  But you gain knowledge, and once you get one glaze working well, instead of paying 50 bucks a gallon commercial glaze you pay 50 bucks for 10 gallons (or more) of homemade glaze.  Take steps to learn this skill, very valuable over time.  But for now, commercial glazes built for commercial bodies is a good starting point. 

I would have called laguna first and asked which clear they recommend for what you are making though.   Some clears don't play well with underglaze for instance.

[Hulk]

fwiw, my experience o' expecting clay supplier's clear glaze (house) to fit their clay was crazed! Per Liam's suggestion, call!

[Min]

Totally fine using commercial glazes if that's what works for your situation, like you said test them on the clay you will be using. Laguna MS29 is a lovely crystal clear glaze but unless they've changed it from about 20 years ago the dry form of it hardpans like crazy. A very small amount of epsom salts solution or macaloid will help avoid this. If you are planning on adding colourants or opacifiers to either base it opens up many possibilities as does using them over underglaze(s).

Like Liam said it does take time to learn about glaze chemistry but to begin with, just learning what each material does in a glaze is a good starting point if you are interested.

 

[BlueSky]

Thanks so much. Good suggestions. I will call Laguna and ask them. 

The other glaze I am interested in trying if my Laguna is a big flop, (and I may actually mix it myself from the recipe - going against my space problems) is the Tony Hansen G2926B. I do recall someone, in some thread not thinking the chemistry made sense...Anyone try it? I just don't get how you know what will work with your clay body. With slip it makes sense to me because you want to use clay that shrinks the same as your clay...How do you know how much a glaze is going to shrink?

 

[Callie Beller Diesel]

The completely unsatisfactory answer that no one in the history of making anything in clay ever had liked is: you have to test it to find out.

You can use software to get your glaze  within a range, but those numbers are estimated. Estimated COE’s are problematic because they’re dependent on a lot of factors, and they’re not always a linear measurement. 

That said: most things that Tony Hansen formulates tend to be chemically sound, and tend to be very good jumping off points for experimentation. They are mostly meant as good base glazes, and few of them make really clear clears, with the exception of his ultra clear recipe (don’t know the number off the top of my head). He designs glazes to work on Plainsman clays, because he works for them. 

 

[liambesaw]

@Callie Beller DieselDoesnt he own plainsman clay?  I have found his recipes to be nothing but trouble on my clay bodies, but obviously they work for others.  That's the joy of glaze formulation 

[BlueSky]

The clearer this becomes the muddier it is! I called Laguna as suggested and I guess I put the cart ahead of the horse because the COE of my clay choices doesn't necessarily line up with the dry glaze I purchased.  I'm going to mix it and test it anyhow. 

This change is really exhilarating. There are a lot of balls in the air. I am trying to develop my style/voice, pick a clay body that I like for functional (since my old sculpture mix 412 is not food  or glaze friendly) and find a glaze that works for with my style and is functional.  

Let's say I land on one or two clay bodies that I want to stick with for awhile. Would you  search for other people that use the same clay and see what their successful recipes are? 

I appreciate all your years of experience and help! Thanks!

[Min]

3 hours ago, BlueSky said:

I just don't get how you know what will work with your clay body. With slip it makes sense to me because you want to use clay that shrinks the same as your clay...How do you know how much a glaze is going to shrink?

It's not how much the glaze is going to shrink but rather what the (reversible) coefficient of expansion of the clay and glaze is. During the glaze firing there is going to be fired shrinkage of the pots in the kiln. As the kiln cools both the glaze and the clay will continue to shrink but very very slightly from peak maturation temp down to room temperature. Clay and glaze are no different than most other materials, they expand when heated up and contract when cooled. Given this expansion/contraction that happens the clay and glaze need to fit each other so they can shrink/expand at the same rate, this is called the Coefficient of (reversible) Expansion (COE) or sometimes called Coefficient of Thermal Expansion (CTE). When a fired pot is used  it will expand when heated and contract when cooled, glaze and clay both have to do this equally, if they don't you can get fit issues. 

Some clay companies will give you an idea of what the COE of their claybodies is but it's not always very helpful. Just knowing if it's a high, med or low expansion claybody is enough to get you in the ballpark when glaze testing. Glaze calculation whereby you get a COE of a glaze is helpful, but only to a certain point. Glaze materials don't always play by the rules because often they don't work in a linear fashion. If you change add or subtract even 1 material in a glaze its COE will very likely be different but higher or lower doesn't mean more or less practical expansion/contraction. If you have an idea of which oxides have a higher or lower COE you can get an idea if the glaze will be higher or lower in it's COE. Example would be a glaze high in sodium (from high nepheline syenite for instance) is much more likely to craze than a glaze with moderate amounts of it or one with an appreciable amount of magnesium (from talc for example). 

Glaze shrinkage on the pot results in crawling glazes, lichen/crawl/reticulated glazes are an extreme example of that.

[Hulk]

Hi BlueSky!

I have a batch of  G2926B; was looking for (much) lower coe - varying degrees of crazing on several clays. While the glaze was an improvement, still much crazing, even after tweaking the recipe some. It does work well on the buff clay that I was using, however, already have/had glazes for that one...

Ended up working off of another recipe; my "looks like this will work" clear (version III in that line) for the problem/craze-y clays has about a third the sodium, and just over twice the magnesium than the  G2926B, also a jolt of lithium, as well as a smidge of Zircopax. Shout if you get craze patterns smaller than, err, quarter inch 'round - pencil eraser size - or are otherwise interested/curious (it's posted here somewhere).

Good on you, reading Tony Hansen - there are simple "solutions" to crazing, however, may not be particularly durable, or clear, or well behaved. Mr. Hansen's site, a trove it is, aye.

[Callie Beller Diesel]

4 hours ago, liambesaw said:

Doesnt he own plainsman clay?

Nope. Plainsman was owned by the IXL brick company until a few years ago, until they divested it because it wasn’t a  (relatively) profitable division for them. They sold it to the Medalta society. Tony is an employee. 

[liambesaw]

40 minutes ago, Callie Beller Diesel said:

Nope. Plainsman was owned by the IXL brick company until a few years ago, until they divested it because it wasn’t a  (relatively) profitable division for them. They sold it to the Medalta society. Tony is an employee. 

They're lucky to have him then