Glaze with variations

[DMCosta]

Hi All,

 

I am all set to begin making my own glazes this week. I am going to start with small 100 gram batches, I have gotten my low fire recipes from Emmanuel Cooper's potters book. There are no glaze making classes available anywhere and my only offer was expensive private lessons. I am a competent person, so I am trying to figure it out on my own. One issue though, on more than one of the glazes I want the variation not the base glaze. I put an example of two below. I have figured out if it has one percentage variation how to factor that in, but what about two or even three? I am terrible at math but my husband is great at it, so although I know it may not be the easiest thing to explain via online, can anyone help out with this? I appreciate any help, Dianna.

 

Opalescent Blue Glaze (one with two percentages)

Spodumene 20

Calcium Borate frit 50

Ball Clay 12

Flint 18

Rutile 3%

 

Variation: 0.75% cobalt carbonate

[Guest JBaymore]

I am not quite sure what you are actually asking.......

 

To take a percentage of any number you first need to convert the precentage factor into a decimal fraction. To do that move the decimal point two places to the left.

 

1% = .01 2% = .02 3% = .03 4% = .04 5% = .05 .....and so on

 

 

Then you multiply the decimal fraction you got by the total weight of the original glaze recipe you want to make the addition (variation) to.

 

So if it is a 100 gram total original batch and the "variation" you want is a 2% addition, you multiply 100 grams by .02 and come up with an answer of 2 grams. Your final mixed batch of glaze will weigh 102 grams.

 

If the total glaze batch recipe was 200 grams......... then you multiply 200 times .02 and get 4 grams addition.

 

 

and so on.

 

 

 

For that .75% value you STILL move the decimal two places to the left....... so it becomes .0075 as a decimal fraction.... then do the multiplication the same.

 

Is that what you were looking for?

 

best,

 

.......................john

[DMCosta]

Thank you for your help John! I suppose to clarify my question I am asking: Can a glaze recipe including the colorants and/or variations add up to more that 100% in total. From what I understood initially the entire glaze recipe including any added colorants/variations still must add up to a total of 100%. However, if I add the extra percentages stated in the recipes, the total percent of the recipe including everything will be over 100.

[neilestrick]

Thank you for your help John! I suppose to clarify my question I am asking: Can a glaze recipe including the colorants and/or variations add up to more that 100% in total. From what I understood initially the entire glaze recipe including any added colorants/variations still must add up to a total of 100%. However, if I add the extra percentages stated in the recipes, the total percent of the recipe including everything will be over 100.

 

The base formula, which is usually white or clear or milky (unless it is a slip glaze), totals 100%. Colorants are always added in addition to that. So yes, more than 100%. It's very common to use different color variations of the same base glaze. For example, I have a glaze in my studio that I use to make 4 different colors:

 

#1: 1/2% Cobalt Carb, 2% Copper Carb, 2% Tin Oxide. Makes a great deep watery blue

#2: 2% Mason Stain (can't remember which one), 10% Superpax. Makes an opaque easter egg blue.

#3: 6.5% Red Iron Oxide. Makes an olive green.

#4: No colorants for a Clear glaze.

 

The benefit of doing it this way is that I know how this glaze behaves so I can control it very well.

[TJR]

DM costa;

I have been thinking about your predicament all day, and have been trying to work out a simple way to explain this. I am not a math guy either. It is way easier to explain glaze mixing by showing rather than telling.

Here goes;

1. You need an Ohaus triple beam balance scale for mixing glazes. Chemistry labs in high schools use them.

2. Look at your glaze recipe as written.

3.Remove the 3% rutile for now. Rutile is your colourant which will give you yellows to golden browns.

4.Add up your materials in your listed glaze.

you have

Spodumene 20

Calc. Borate Fritt 50

Ball Clay 12

Flint 18

-----

100

5. That is your base. All glazes add up to 100% with the colourants removed.

6. Get three styrofoam cups

7 Mix up three base glazes, as in put 20 grams of spodumene in each cup, then50 grams borate fritt in each,then ball clay12 grams,then 18 grams flint.

8. Mix up with water. Seive the first one. That's you base. Apply to a test tile.

9. To the second cup add 3 grams of rutile. That is 3% of the total of 100 grams

10. This is where it gets tricky.0.75% cobalt carb is less than one gram of cobalt. Cobalt is a very strong colourant. Most blue glazes call for one half of a percent or 0.50 of a gram. This is why you need the Ohaus scale for these very small increments.Your third test add cobalt carb to the third cup with your base glaze.

11. If you want 1000 grams of glaze instead of 100 gram cup size, you add a zero to all your numbers.For example;

Spodumene 200

Cac. Borate fritt 500

Ball clay 120

Flint 180

Check to see if your recipe adds up to 1000

Then add Rutile 30 grams

or cobalt cab 7.5 grams.

 

For 5000 grams, you multiply all of your numbers by 5, after you have added the zeroes to all the numbers. So that would be 1000 grams of glaze times 5 equals 5000 grams or a bucket of glaze.

Use a calculator and write it down. Don't talk to anyone while you are measuring, and use a dust mask.

 

I hope this helps.

TJR.

[Marcia Selsor]

TJR

That is somewhat like what my classes use to do for color blends. I gave them a worksheet but here was the difference.

 

Using 6 cups A,B,C,D,E, and mixing cup. . Mix 250 grams of base glaze, add to water, sieve, and divide evenly into the first 5 cups putting 50 grams of the base into each cup. Then I would assign colorants into the last four cups. This is just an example:A=Base without colorants. B= 5% Red Iron Ox., C=1% cobalt carb, D=3% Rutile, E=3% copper carb. Add to the cups and sieve cups

Have 15 test tiles numbered 1 to 15

First row A=1 B=2 C=3 D=4 E=5

second row add teaspoon of A with teaspoon of B into mixing cup and apply to test tile 6. The is A+B on 6 A+C on 7, A+D on 8, A+E on 9

third row B+C on 10, B+ D on 11, B+E on 12

Fourth row C+ D on 13 , C + E on 14

Fifth row D+ E on 15

You end up with 15 separate colors.

You should also test the combination of all the colors.

Marcia

[TJR]

TJR

That is somewhat like what my classes use to do for color blends. I gave them a worksheet but here was the difference.

 

Using 6 cups A,B,C,D,E, and mixing cup. . Mix 250 grams of base glaze, add to water, sieve, and divide evenly into the first 5 cups putting 50 grams of the base into each cup. Then I would assign colorants into the last four cups. This is just an example:A=Base without colorants. B= 5% Red Iron Ox., C=1% cobalt carb, D=3% Rutile, E=3% copper carb. Add to the cups and sieve cups

Have 15 test tiles numbered 1 to 15

First row A=1 B=2 C=3 D=4 E=5

second row add teaspoon of A with teaspoon of B into mixing cup and apply to test tile 6. The is A+B on 6 A+C on 7, A+D on 8, A+E on 9

third row B+C on 10, B+ D on 11, B+E on 12

Fourth row C+ D on 13 , C + D on 14

Fifth row D+ E on 15

You end up with 15 separate colors.

 

Marcia

 

Masrcia;

Thanks for the input. I was trying to get the idea across that DMcosta already had a percentage in that the glaze totaled 100 grams without the rutile.

I was not going to get into line blends, as in 0.25 cobalt,then add another 0.25%, and then another as a line blend.

I don't know if my message was understood or not. Hope so. Thanks for taking the time.

TJR.

[Marcia Selsor]

TJR

as you know simple color blends can really expand the pallete.

Marcia

[perkolator]

The base formula, which is usually white or clear or milky (unless it is a slip glaze), totals 100%. Colorants are always added in addition to that. So yes, more than 100%.

 

I believe this is the answer you're looking for.

 

for that particular glaze you wrote in the 1st post - the variation would be 0.25% Cobalt (light blue glaze) instead of 3% Rutile (tan-ish glaze). Another variation might be having BOTH 3% rutile and 0.25% cobalt, which might give you a variegated surface since rutile has a tendency to do this to glazes. colorants and opacifiers are almost ALWAYS added on top of the 100% base glaze, unless otherwise specified in the recipe.