I recently ordered some CMC from a supplier that had taken advantage of a good deal.
A colleague of his owns a large food service supply facility, and contacted this ceramic supplier saying that some “food-grade” CMC had been returned to him. For various reasons, he couldn’t sell it again within his usual market, so they made a deal on about 1800lbs of the stuff.

I had created quite a thick/viscous gel from this recent CMC powder, using the same measurements that would have yielded a much thinner liquid with the CMC product that I’m used to.
I was told that this “food-grade” CMC was many times more pure than other types. I also learned that lesser grades will actually add finely sieved, but otherwise unaltered, wood pulp –and therefore have less of the gum forming properties.
I had to dilute that gel 7 more times with straight water to get it to a usable state. I could have probably diluted it a little less, or even a little more, depending on my method of glaze application, but I’ll run with this concentration for a bit.

As long as it works for me, I’ll certainly be ordering more of it –getting anywhere from 5-10 times as much product for the same “market price” of CMC (@$8-10/lb.) would be great.

As there are probably many grades of CMC available, I have rewritten the information in the page above to reflect this, offering the: “0.5-2.0grams CMC : 8ounces H2O” suggested dilution rate.

~jesse.

To get more accurate, we’ll need to rid ourselves of that silly American standard of measurement:
5 cups = 1200ml (oooo, a nice round number… ain’t that nice? Man, that almost NEVER happens).

25g CMC into 1200ml H2O means that there is 5g of CMC per 240 ml of H20.
If 60ml of that solution is added to 100g of dry ingredients, then 1.25g of CMC is now part of that glaze.

In terms of diluting it again –let’s start over:

6 cups = 1440ml H2O
5 cups = 1200ml H2O
25g CMC into 2640ml H2O means that you have 5g in 528ml –or almost 0.0095g CMC per ml H2O.
If 60ml of your final mix is added to 100g of dry ingredients, that means 0.57g of CMC is in that glaze… again, that’s about half as much as I use.

Now, if you meant that you dilute it by 1/6:
1/6 of 1.25 = 0.2g CMC
Wow, that’s not a lot… (Added note on April 24, 2008: See the comment below this one).

In James Chappell’s “The Potter’s Complete Book of Clay and Glazes”, most of the glaze recipes follow with “add 1 tsp. CMC”.
Yeah… off the top of my head, I couldn’t tell you what 1tsp. of CMC weighs in at, but Jeff Zamek steps up in “What Every Potter Should Know”, by referencing between 0.125%-2.0% dry CMC powder by weight in a glaze. Keep in mind, however, that most of the glazes listed in Jeff’s book had a clay content of 4% or higher -or asked for bentonite.

Kris Friedrich also lists bentonite in his recipes, while John Tilton often adds EPK, so both would understandably use less CMC than I.
For the example recipe in this post, I said to use Bentonite OR CMC.
So, what’s the clay/bentonite situation at Greendale?

Speaking of which, make sure y’all check out Holly McKeen’s site.

Hey Jesse… My recipe from Kris’ has this same amount as you quote to form the CMC solution, that is then diluted 1 cup CMC solution to 6 cups water… I don’t see you mentioning the dilution. Are you saying you use it that thick straight into your glaze?
i.e. ….. you say above “CMC as an example then, I often add 25-30 grams of dry CMC powder to 5 cups of water. The amount of CMC needed will depend upon your glaze. Blend the powder with warm/hot water until mixed, let it sit for an hour or so, and blend again before use. This pre-hydrated gum solution is mixed with the dry glaze batch to produce a usable consistency (52-72% of the dry glaze weight works well in my crystalline bases).

I am finally working on getting my specific gravity right for every single glaze… I usually just start with about 60% cmc/water solution and take it by feel, but I’ve been getting it a bit thin (mistake) lately, so I’m finally deciding to get more particular about the measure…