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What makes this glaze tick?


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Below is a glaze recipe i have been using lately and which i like very much. Its very stable, has a nice semi matte finish, and the pretty green/blue color is “varigated”(?).. (see below)

i would like to understand the recipe better with an eye towards changing the color but retaining the other characteristics. 

Toward that end i have mixed up a new batch but have omitted the copper carb and the titanium dioxide (which i understand to be a pure form of rutile?)..  i hope to add some different colorants  

my questions:
1. Am i correct that it gets its color from the copper carb AND the titanium dioxide?
2. if i want to change colors but retain the “varigation” quality do i need to change out the copper carb but keep the titanium dioxide?  In other words, is the titanium dioxide contributing color? Varigation? Both?

3. any suggestions for alternate colors? (cobalt blue of course)

as always — thanks for any advice you can offer  

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I’ll take a stab at this, hopefully it helps a bit:
Here is what I can say, the colorants are copper and titanium and ..... they are likely a very small quantity of the entire recipe. Generally colorants are added in small quantities with respect to the total ingredients to produce the color and effect desired.

Titanium dioxide is a thing, rutile is mostly titanium dioxide but also contains a minor amount of  some element or elements, contaminants if you will........... usually iron.

A simple view is: glazes are made of silica, alumina, fluxes and colorants. Silica and alumina melted together form a glass but they don’t melt on their own till the temperature gets to be 3000 f degrees or higher. Fluxes help them melt earlier which is called a eutectic point. The geology of the earth  basically melts at cone ten, so on planet earth when we make glazes and use things we mine from the earth they basically start as cone ten and we use fluxes to get them to melt nicely when we want them to. (Cone ten or earlier)

Fluxes often affect the colorants  ....... and colorants can also affect how the recipe melts. Color theory is very complicated in that colors can appear brighter, lighter, darker etc.... depending on their interaction with fluxes.

So ...... immensely complicated with respect to variability and most often requires testing to see which ranges of colorants in a particular recipe yield the desired look.

So in very general terms copper carb gives you the green, the titanium affects the color and likely gives you the variegation. Changing the percentages of these (colorants) will vary the color and effect.

Over time folks learn the trends in interactions of these things which again is extensive with respect to variability so line blend type trials are usually the way they dial in their color. This is generally done by changing one component in strength at a time. . Often changing one component at a time is the best way to isolate an effect within a reasonable range. Changing two of them simultaneously often makes the process more random and less predictable because of the possible interdependency of everything.

Edited by Bill Kielb
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Bill

Thanks.  All very helpful.  A "line blend" problem I keep encountering and that I cant seem to get comfortable with:

 OK.   I have a 10,000 gram batch of the above recipe (but without the colorants) and i want to do a line blend.  (Of course the 10,000 grams is the dry weight of the ingredients and i have added unknown amounts of water)  I need to measure out small portions of the liquid glaze in which to do the line blends.  For instance, 10 small cups each containing 100 grams of glaze.   How do I then calculate how much colorant to put in each? 

If I say that this cup is 100/10,000ths of the total (i.e. 1/100th), I am ignoring the water weight  aren't I?  

How do I calculate this colorant "add" number?

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Having laid out the problem like that in the above, it now seems a little clearer to me.  I guess i need to measure out the colorant needed for a 10,000 gram batch (dry weight), and then add 1/100 of that amount to each cup?

As in:

  1. Recipe calls for 2% colorant
  2. 10,000 gram batch needs 200 grams of colorant.
  3. each 100 gram cup gets 1/100 of 200 grams or 2 grams.

??? Right ???

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48 minutes ago, Rick Wise said:

Bill

Thanks.  All very helpful.  A "line blend" problem I keep encountering and that I cant seem to get comfortable with:

 OK.   I have a 10,000 gram batch of the above recipe (but without the colorants) and i want to do a line blend.  (Of course the 10,000 grams is the dry weight of the ingredients and i have added unknown amounts of water)  I need to measure out small portions of the liquid glaze in which to do the line blends.  For instance, 10 small cups each containing 100 grams of glaze.   How do I then calculate how much colorant to put in each? 

If I say that this cup is 100/10,000ths of the total (i.e. 1/100th), I am ignoring the water weight  aren't I?  

How do I calculate this colorant "add" number?

Most folks will just mąkę it easy on themselves and mix 100 grams of glaze dry then dilute , no colorant and progressively blend from there so it translates easily back when a good percentage of a colorant is found.  So for me, mix 100 g of dry no colorant, add water, then mix colorant in grams starting low and going high. Dip test tiles into each mix as I go, label tiles with UG pencil.

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I think you are making it more complicated than it needs to be for a simple colour test. Weigh out 100 grams of base then add the percentage of colourants you want to test. If you are going to test just one colourant at a time just do a simple progression test where you increase the amount of just the one colourant. For example, 100 base glaze + 5 titanium dioxide + 2 bentonite + 0.25 cobalt carbonate (just for example). Mix it up, sieve it then dip a test tile. Now add another 0.25 cobalt and dip another test tile, repeat up to 2 total of cobalt carbonate. This way one test batch will give you 8 shades of cobalt blue.

I would actually add the titanium and bentonite to your base so you don't have to weigh it out for each colour test, your base glaze for colourant testing would then weigh 107. For a fairly extended colourant test like the cobalt blue example above I would double your base (and double the colourant) so you have enough glaze slurry to work with. Each test is going to be slightly off as you are decreasing the base amount of glaze with each dip but it will get you in the ballpark.

12 hours ago, Crooked Lawyer Potter said:

Toward that end i have mixed up a new batch but have omitted the copper carb and the titanium dioxide (which i understand to be a pure form of rutile?)..  i hope to add some different colorants

Rutile can make a lovely tan /gold coloured glaze, could be worth testing the base with that in place of the titanium dioxide. To get the same amount of titanium in the glaze bump the rutile to 5.5

After you get this sorted you could try a 2 colourant blend or a triaxial, they more complicated but will give you a palette of blended colourants. Reason this is sometimes worth doing is because some colourants (like cobalt) can look better when modified slightly with some iron or manganese. 

(BTW, I removed your extraneous posts where you were having problems attaching the image)

 

 

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52 minutes ago, Rick Wise said:

Having laid out the problem like that in the above, it now seems a little clearer to me.  I guess i need to measure out the colorant needed for a 10,000 gram batch (dry weight), and then add 1/100 of that amount to each cup?

As in:

  1. Recipe calls for 2% colorant
  2. 10,000 gram batch needs 200 grams of colorant.
  3. each 100 gram cup gets 1/100 of 200 grams or 2 grams.

??? Right ???

The beauty of 2%, if true is it’s always  2% — so 2% of 10000 gram dry batch is 200 grams color. 2% of 100 gram dry batch is 2 grams of color. Easier to think of it as dry perhaps so concentration is easier to envision. Ignore the water.

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@Rick Wise Yep that is Pete Pinnell's Strontium Matte. If I tested this it was 12 years ago. I use Pete's  Seafoam glaze all the time - it looks a lot like your picture, but it is a different glaze than the Strontium Matte.  BTW try your glaze over Strontium Crystal Matte Cool - a very reactive glaze - you will get some exciting results - watch out for the thickness of the SCMC - things will run if to thick. Here are some colorants I have in my notes for Pete's Strontium Matte.

copper carb - 5; titanium dioxide - 5

copper carb - 0.5; titanium dioxide - 0.5

copper carb - 6; rutile - 4

cobalt carb - 1.5; rutile - 4; red iron oxide - 2

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