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#1 Pam S

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Posted 26 July 2013 - 01:19 AM

This may be obvious to some, but not to me. Why do most formulas list multiple ingredients that total 100% and then the "add"? The OCD part of my brain thinks the 100% is a base that can be altered by the add (I may have answered my own question). If that is the case, why isn't the initial formula identified, i.e., white gloss, beige matt...

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#2 Marcia Selsor

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Posted 26 July 2013 - 06:59 AM

The base glaze is converted to 100 so that adding various colorants is easier.
Comparison of ingredients with other glazes .
And a quick look at a recipe will let you know if it is balanced or not...high in silica or low in clay, etc.
You know after experience if you have enough of an ingredient in stock.

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#3 bciskepottery

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Posted 26 July 2013 - 07:11 AM

The base glaze establishes the durability and fit of a glaze to your clay; that remains the same regardless of the combination of oxides and colorants added.  It also gives you a solid base to develop a color palette.  If you look at Mastering Cone 6 Glazes by Hesselberth and Roy, you'll see they start with a series of different base glazes that give you various surface types (glossy, semi-glossy, semi-matte) and then add various oxide combinations to produce different colors or variations of the same color.



#4 Bob Coyle

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Posted 26 July 2013 - 10:08 AM

You are right Pam they should add all the ingredients in, but the convention has become that of listing the base glaze first and then adding colors and thickeners. The fact is that adding oxides and colorants can change the way the base glaze works. Large amounts of iron oxide for instance will serve not only as a colorant but a flux.

 

Of course the moral of the story  for all  formulations is to do tests on all new glaze mixes before you use them on your pots.



#5 neilestrick

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Posted 26 July 2013 - 10:17 AM

Most colorants will not affect the glaze melt. Some, like iron (primarily in reduction) and copper can, but only in higher amounts, so it's not really necessary to include them as part of the glaze formula. Like the previous posts said, adding colorants on top of the 100% allows for easier comparison of glazes, and gives you the option of adding your own colorants without having to recalculate the batch.


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#6 oldlady

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Posted 26 July 2013 - 11:36 AM

all of the above, just adding this.

 

you will see many glazes named by a color.  RUTILE BLUE for example.  doesn't mean that the base glaze recipe cannot be used by itself.  sometimes the base is a great glaze which comes out a soft color of some kind not at all like the one you get when you add the cobalt or whatever is used to get the blue.  this base glaze will look different on various clays, my white body might produce a pinkish color while someone else using a reddish clay would see no particular color.  testing base glazes without added color can be very interesting.

 

i have begun mixing up the dry ingredients and labeling the bucket with the name of the glaze and a note  BASE ONLY.  that way i can take some out of the 5 gallon bucket, weigh out maybe 500 grams, add a percentage of colorant to that amount and water and do only one pot in that color, saving the bulk of the glaze for use with other colors. "base only" tells me that it is not yet blue so if i want blue i have to put in the cobalt.

 

i really want to try a new one from my friend Robin Teas.  it is a lovely matte mid-purple called  Reliable Purple.  i know it will make other colors that are equally good.


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#7 Celia UK

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Posted 26 July 2013 - 02:00 PM

From one 'old lady' to another - this has raised a question that I've pondered several times. If you weigh out 500 gm of your base glaze how do you know the weight of the dry material it contains, against which to calculate the % of your colourants? In my understanding, when a recipe says, for example 3% cobalt carbonate, that is 3% of the dry base glaze ingredients. However, once mixed with water, you wont know how much dry material is in your sample. I'd like to do just what you're suggesting for my tests - mix a quantity of base glaze then take out small quantities and add various % of colourant so I'd be really interested in how this works.

#8 neilestrick

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Posted 26 July 2013 - 02:55 PM

All weights should be done as dry batches, as there's no good way to know how much material is in a wet batch. But you can mix up a larger batch of glaze, say 1000 grams, then measure out 5 equal cups of wet glaze to add colorants to, knowing you've got approximately 200 grams of dry material in each cup. It's not as accurate as dealing with dry weights alone, but good enough for a first round of color tests. You could also dry mix that 1000 grams very well, then weigh out dry batches from it.


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#9 oldlady

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Posted 26 July 2013 - 02:59 PM

celia, it is my failing that i think in terms of mountaintops and forget that to those unfamiliar with a process have to go down one and climb the next.  sorry.  i also think the computer knows when i finish a thought and it should put the stuff here without my doing the silly thing called POST.  will i ever learn???????

 

mixing ingredients dry results in a bucket full of dry powder.  this stuff is a base glaze.  it just doesn't have water in it yet.  our language doesn't give us a word to describe which thing we are talking about unless we remember to say DRY when describing the powder state.  if you mix everything up with a drill and mixer while wearing a respirator, you can sieve these ingredients while they are dry and store them.  that way, each time you use any of the base glaze to make a particular color, the ingredients are correctly proportioned.  

 

in my example, if i have 500 grams and need 2% cobalt i just (because i am REALLY bad at math) add 2 grams 5 times and get 10 grams.  i put this into the 500 grams of base and add distilled water until i think it is right.  getting the proportion of water is a hard one, many discussions here about THAT subject!  one way is to put the amount you think you need in a cup and add it slowly while mixing with an immersion blender until the consistency seems right.  if there is leftover water in the cup, it is ok.  if you need more, it is ok, too.  i use distilled water because my tap water has an enormous amount of calcium in it.

 

i typed a better answer to this just a minute ago and lost it because i did not hit POST,  i hope i do it right this time.  i see that neil has gotten an answer in during my lapse.  i also edited the previous post.


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#10 Celia UK

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Posted 27 July 2013 - 10:48 AM

Thanks to both posts above. Neil's answer was where I had got to myself and this was fine as long as I made accurate records, in case I wanted to go back to my 'wet' base glaze for more tests at a later date.

And thanks Old Lady knowing that experienced potters refer to the dry mix as the base glaze will make other posts make more sense in the future. For some reason, the word glaze had always said 'liquid' in my head, now I know better. EXACTLY why the forum is so helpful!

#11 Pam S

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Posted 28 July 2013 - 02:21 AM

Thanks for all the replies! I have so many things to try! Every batch I mix will now have a test tile done before the "add."

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#12 Marcia Selsor

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Posted 28 July 2013 - 07:46 AM

somewhere in the archives I have a description of how to do a 15 numbered tile color blend with 250 grams of dry base and 4-5 colorants.Mix with water then you separate the 250 grams into 5 plastic cups. Add colorants for example:
A nothing or something like 3% rutile
B 1-3% cobalt Carb
C 2-5% iron oxide
D Copper Carb 1-4%
E rutile or a stain, tin what ever

First row 1-5 is straight from the cups. 50 grams would mean 1/2 of the mentioned percentage ex. 5% = 2.5 grams
Second row 6-9 mix a teaspoon of cup A with a teaspoon of each of the other
Third row 10-12 mix B with the 3 others
Fourth row 13, 14 mix with C
Fifth row 15 mix D and E
You get 15 different colors in your base. I seive after adding the colorants using a small sieve.

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#13 Pres

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Posted 29 July 2013 - 08:06 AM

When working with HS kids doing glaze mixing and experimentation we would mix 500 to 1000 grams of a base glaze, then each student would do a line blend using the base and add in an oxide of their choice. this allowed them to understand the base mixing, and the purpose of the oxide in coloring the glaze. After that we tried using the base in a blend with an opacifier on one end, and an oxide on the other. We never ended up doing tri or quad blends, as they could not wrap their heads around the concept in the time I had with them.


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