douglas gray on wed 14 jan 98
Considering the time we live in, simplicity is hard to come by, and therein
might lie the allure of simple glazes. There is something comfortable, if not
pleasurably primitive, in using a simple combination of ingredients. It is
effiencient. It is easy. It may produce some very intriguing results.
Many of my replies to the list come from the teaching point of view, probably
because I spend a great deal of my time teaching. This one will be no
different, so tune out now if you don't want to hear another lesson on how to
formulate glazes, the simple way. No chemistry, I promise.
Let me first state that I agree with Ron Roy about the nature of complex glazes,
that they are more refined and controllable and make for better all-around
glazes. Having said that, though, there are a few reasons I pursue simple
glazes. The first and primary reason is that they make an excellent place to
begin discussing glazes with a group of people that don't know the first thing
about glazes. Actually, I start even one step before that. I start with the
single ingredient.
The first glaze test my beginning students do involves one material from the
list we have available in the lab. They measure out one teaspoon, pack it tight
so it holds its shape and then they turn it out onto a clay pad. It is
important that the mound of material stays in the shape of the measuring spoon
(sea shell, or whatever measure you happen to use). We mark the clay pad with
red iron oxide so that we know which material is which and we run them through
the kiln with next glaze firing. It doesn't matter what temperature you fire
to, just run them through with a regular load, what you normally do. This will
let you know what those particular materials do, in your kiln, in that amount of
time, with that amount of heat. Then you look at them, noting which ones, made
glass, which ones spilled over the clay tile, which ones got hard, which one's
shrunk, which ones broke the clay tile, which ones didn't change at all. With
these tests, the differneces are not just some abstract thought that floats in
one ear and out the other, but the differences are visual, easy to see.
Then we seperate all the tiles out according to the following classification,
flux, alumina (clay), or glass former. Some of the ingrediants will fit in more
than one catagory. If you don't know which catagory they fit into, check any
ceramics manual. We use Robin Hopper's CERAMIC SPECTRUM because its handy and
available.
Then I give them one basic premise to go on--that most glazes have all there
catagories represented. The glass former helps produce glass, the more you have
the thicker the layer of glass can be. The alumina helps keep the glaze stuck
to the clay body, you need at least 5-10% to get a good adhesion. And the flux
helps melt everything together and determines the ways colorants will respond.
So the next test is simple. We select two ingredients, making sure that all
three catagories are represented and we do what is called a line blend. Since
we know what the ingredients will do by themselves, it's time to see what they
do in combination. We measure our ingredients by weight, because its simple.
So if you take 80% ingredient A and 20% ingredient B, you will get one
combination and it will make a glaze, but it might not be the best glaze. So
then you take 20% ingredient A and 80% ingredient B and you make another glaze.
Then you dip your tile into each of these, making sure you mark them in some way
so that you will know which is which. And just for kicks, we pour the two
glazes together and that gives us a 50/50 batch we can test too.
So we fire the tests and some where along that line blend we get the makings of
a glaze--a simple two ingrediant glaze. Maybe the 80/20 batch is too runny and
the 50/50 batch is too dry, well you can do another line blend except this time
you try 75/25, 70/30, 65/35 and 60/40. After the next firing you have narrowed
it down to the best combination of these two ingredients. At this point you
have a glaze, but you're not done.
The next test is to add colorant, maybe an opacifier, maybe you want to correct
for crazing, maybe you want to add another flux so that you can get that color
you've been after all semester. Pretty soon you've done twenty tests, the
semester is over and you still haven't gotten the glaze just right, but its
better. That simple glaze is more complex, maybe you are up to four
ingredients, maybe five or six, but you've narrowed the results down to
something usable, something nice to the touch and pleasant to the eye.
And then you start to think, simple glazes are not always so simple. Maybe Ron
Roy was right after all.
I use simple glazes all the time as a starting point. The key to any kind of
glaze testing, though, is to test the glazes. Never think you don't have enough
know-how to change a glaze. If you can make a box cake you can mix a glaze and
if you can mix a glaze you can change it, simple enough.
Then, maybe you'll even have determination to change that standard glaze you've
have used for the past twenty years, making it a bit smoother to the touch or a
bit less blue or maybe stopping it from running so much. If nothing else,
manipulating these simple two or three ingredient glazes might just give you
confidence to tackle one of those complex glazes. Who knows you too might
become a clayart glaze guru and have to pay $15 to wear a techie badge at the
clayart hospitality room at NCECA.
doug
============================================================================ =)
Douglas E. Gray, Assistant Professor of Art
P.O. Box 100547
Department of Fine Arts and Mass Communication
Francis Marion Univeristy
Florence, South Carolina 29501-0547
dgray@fmarion.edu
803/661-1535
douglas gray on sat 17 jan 98
In message "douglas gray" writes:
> Bonnie, you had a good question, so I hope you don't mind me replying on the
> list--to clarify the process for others who might be "trying this at home."
>
> Mixing those line blends does take some time to do. The key is to use the
> mixed batches as many times as possible so you do less mixing. This may get
> a little confusing, so hang on to your hats.
>
> To get the best combination of two ingrediants you would ideally like to see
> how the combinations work at regular intervals. For example
>
> ingredient A 90 80 70 60 50 40 30 20 10
> ingredient B 10 20 30 40 50 60 70 80 90
>
> That is a lot of mixing. So, when I mix up a line blend I try to use the
> same batch over again whenever I can. I typically use the following example,
> leaving out the most extreme ratios of 90/10 and 10/90 (these ratios are so
> close to the pure ingrediant test that I don't see a need to use them).
> Let's say you mix up the 80/20 version and the 60/40 version, and dip a test
> tube into each. I would then pour those two glaze batches together and that
> would give me the 70/30 combination without having to weigh it out. Let's
> say that you do the same thing at the other end of the line blend. You mix
> up the 20/80 version and the 40/60 version, dip your test tube and then pour
> these two batches together to get the 30/70 version. If you take your 70/30
> combination and the 30/70 combination and pour them together you will get you
> 50/50 version without mixing it. So in essence you mixed up four tests, but
> you get an additional three test combinations for free.
>
> Testing does take time, and for total accuracy I would weigh each step out.
> But when i am trying to come up with a rough idea of what will happen, I do
> the mixing procedure. I typically only mix up 100 gram batches when I do a
> test, so I'm not wasting to much of the materials. Mixing amounts this small
> does require extra care in measuring. A few extra grains in a one ton batch
> doesn't make any difference at all, but a few extra grains in a small batch
> could skew the results. So, as always weigh twice and cut once, or something
> like that;).
>
> Another thing I do that may be different from the norm (who is this Norm any
> way?). Rather than rolling out a slab and cutting out test tiles, I cut out
> four by four inch squares and roll them around my finger to make a tube. I
> use a tool or stamp to create some texture on one portion of the tube and if
> I'm really on the ball, I brush a thin stripe of white slip up the side.
>
> Is this retentive? Probably, but it tells me several things. First, the
> test tube (fired on end) gives me some kind of idea how the glaze responds to
> vertical surfaces. If I only made plates, the tiles would work fine, but the
> tube gives me a vertical surface and a nice edge at the top to see if the
> glaze breaks. Next, the texture is there so that i can tell if the glaze
> will cover it up or let it show through. Nothing worse than carving on a
> piece for three days and them applyin the wrong glaze and covering it all up!
> (YIKES). Finally, the strip of white slip gives me a reasonable idea of how
> the glaze would look over a clay body low in iron, like white stoneware or
> porcelain. Just to get that last little bang out of my tests, I double dip
> the test when I glaze so that i can see the difference between a thin and
> thick application. Let me explain this one. You hold the end of the test
> tube in your hand and dip it into the test glaze to the half way mark, let
> that dry just a moment and then re-dip it, only this time just dip a third of
> the tip into the glaze. The area of overlap will give you a thicker coat.
>
> Now if you were to prepare all your test tubes in this manner and dipped them
> all twice and did the line blend, you'd have a very good idea of how the
> glaze responds. The only other thing I would suggest doing would be to
> repeat the test several times, so that you could have tests of the same glaze
> dispersed throughout the kiln. (I am not such a masochist, I only do this
> with glazes when I am positively sure I want to make a committment). Then you
> are really cookin'. You know that glaze pretty well, at least until your
> supplier changes one of your ingredients and, well then... it's back to that
> line blend stuff again.
>
> Testing doesn't have to be difficult. I throw in a lot of extras that seem
> like a lot of work, but to me it is easier than loosing plates, cups, bowls
> etc. just because you didn't know how the glaze would repsond.
>
> I hope this hasn't turned anyone off glaze testing. I actually enjoy it and
> if Won can Cook so can you!!!
>
> doug
>
> In message Bonnie writes:
> > Doug-
> >
> > Thanks for taking the time to share what is essentially your Glazing 101
> > lesson plans with the group.
> >
> > It's making all those line blends that always seemed like it would take a
> > lot of time. All that weighing or mixing. Do you have a favorite
> > technique for making fast blends?
> >
> > Bonnie D. Hellman
> > Pittsburgh, PA
============================================================================ =)
Douglas E. Gray, Assistant Professor of Art
P.O. Box 100547
Department of Fine Arts and Mass Communication
Francis Marion Univeristy
Florence, South Carolina 29501-0547
dgray@fmarion.edu
803/661-1535
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