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preeta

Test Tiles Vs Test Pots For Glaze Combination Tests

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Do you prefer test tiles or test bowls/pots for glaze combination tests?

 

i believed test tiles were the way to go until the school tried out test bowls last fall.

 

i find those small bowls gave me a better picture than the test tiles did. 

 

i understand why one does test tiles - the practicality of it, but does it truly give a truer picture than a test bowl?

 

in a couple of instances the test bowl did not reflect the tile. it was a glaze combination a few of us were trying and weren't able to replicate the tile. then we saw the test bowl and even that did not replicate the tile either. the dramatic contrast on the tile just did not happen on the bowl.  so they did another test tile and boom. was same as the first test tile. 

 

Those test bowls were thrown out mid Spring to make more space for glazing as the classroom had no place to display the test bowls.  

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You really should test on the kind of shape you will be glazing.  No point testing on a horizontal test tile if you're going to glaze a tall straight vase.  Make mini-versions of your finished item then test that.

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Well, glaze is pretty well influenced by gravity. The inside and outside of a bowl done in one color may show this clearly. Some glazes break on texture and may develop a different feel when given larger space. Can you actually show all these features in one test?

 

Test tiles are excellent for testing. But they don't really show the full story. They will show general qualities such as surface finish,  necessary thickness, and response to textures. I don't find them to be a very accurate indication of what the larger surface will look like. I find them more useful for tuning a base glaze and less useful for fine tuning the color.

 

I make bottles with a dent and three strings of clay (enough to spell out letters :-) ) for visual tests. But these require a 3000 gram batch to cover with a pour and dip (the method I usually apply glaze). And displaying different combinations that work well would take too much space.

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The wife uses cylinders she has one of our students make (2 1/2" diameter).  Another studio uses cylinders about the same size but cut in half and hung vertically on the wall. If you hang them, make sure you poke the hole in the middle of the top. I wanted to hang them like wind chimes somewhere but I don't think it could have been an option so I didn't say anything.

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Back in glaze calc class in the early 70s we where taught to make forms that have both vertical and horizontal surfaces. Bowls are to large to fit well in most kiln loads for tests .You can throw some small pie dishes and cut them into small pieces like a pizza. Put a hole in them for hanging when done. You can double dip the lip and see how that runs down as well. You can extrude this and as well and fold a 90 degree bend in that shape or extrude the form with a 90 into it already.

These tests should be small enough not to displace other pots in a load. its best to fire two samples of each glaze test-one cooler and one hotter if you have that chance when loading.

You need to be as scientific as possible with tests and yes they will look different than larger forms but thats the way it is.If you do this testing (which takes lots of time) you will learn a lot from it.

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mark i am learning 'scientific' has a whole new meaning in the ceramic world. luckily for me the testing is sorta being already done. i just have to keep my eyes open. i am looking all around me at how other student's work is turning out. i just happened to notice this at the end of spring when i saw someone's teapot glaze result was quite different than the other person's vase form result. of the same glaze combo. 

 

another question. can you look at a glaze formula and kinda sorta guess how it will turn out? just like a food recipe where you can look at the ingredients and guess how the flavour will be and so you eliminate it before you cook it.  or do programs help you with that?

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Well, what are you trying to achieve with your testing? Are you changing the recipe? Just looking for a sample piece?

 

There are some guidelines for glaze making. Things like the Al:Si ratio can give an indication of glossy vs matte. And other little details -- which may or may not -- help avoid disasters and point a recipe in a good direction.

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I just attended a one day John Britt workshop.  He had 5 tables set up with over 2100 (I did a rough count) test tiles, carefully grouped by base glaze (Marcia, 2 of these were "Selsor" bases), clay type, and colorants. Oh, and oxidation vs reduction.  He also had more boxes with him that he hadn't set up!  Now that's the king of test tiles!

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Well, what are you trying to achieve with your testing? Are you changing the recipe? Just looking for a sample piece?

 

Matthew i am just trying to understand the basic principle of glazing as i dont have access to a glazing class. things like as you pointed out the Al/Si ratio. 

 

Right now i dont want to start with glaze making yet. (i just want to get better at throwing first since i dont have a wheel at home, but i can read up on glazing at home) i am just looking for a sample piece. i have access to 18 glazes that the school has made. ^6 and i am discovering that the glaze combo looks different on different forms. which was a shocker to me as i expected the glaze combo to look the same on the test tiles and the forms, with of course some variation due to thickness or application. 

 

i am reading hamer book to understand the ingredients that our school uses. things like whiting and wollastonite vs talc and dolomite. just getting the basic concept of glazing by just studying what i have access to instead of adding new ingredients. 

 

plus i am also part of a raku club and i really have no idea what i am doing there. 

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I would think that the shape of the test tile would have a significant influence on the outcome of the test. John Britt uses an extruded test tile that should work to give you the outcome you'd expect from a vertical surface with grooves and ridges.

 

BTW Preeta, I see you are located in Sacramento. I live in Citrus Hts. Where are you taking classes...ARC, Sierra or Alpha Fired Arts?

JohnnyK

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johnny i just moved to arden arcade area and am taking classes at SCC. i have not checked out ARC yet, but here at SCC the professor allows me complete freedom to do what i want, how many i want as long as i do the classwork too. 

 

we do have vertical surface with grooves and ridges which work well with one glaze but when glaze combo happens it does not work that well. 

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