Monday, January 28th, 2008
Hydrating the Glaze:
To hydrate a glaze for application whether it be by brushing, spraying, dipping, etc., you need to achieve the same result each time you go to glaze. Every glaze is going to act different and require varying levels of water content to get the consistency that works for you.
When I discussed the reading of a glaze recipe in another post, I left off with this example:
Frit 3110: 51 (x 7.5) = 382.5 grams
Calcined Zinc Oxide: 23 (x 7.5) = 172.5 grams
Silica: 22 (x 7.5) = 165 grams
Grolleg Kaolin: 2.5 (x 7.5) = 18.75 grams
Alumina Hydrate: 1.5 (x 7.5) = 11.25 grams
To get the dark blue glaze pictured on pg. 137 of John Britt’s book, add:
Cobalt Oxide: 3 (x 7.5) = 22.5 grams
Manganese Dioxide: 3 (x 7.5) = 22.5 grams
Red Iron Oxide: 3 (x 7.5) = 22.5 grams
Bentonite (or CMC as a binder): 1 (x 7.5) = 7.5 grams
This glaze has 750 grams of the base + 75 grams of colorant and binder = 825 grams.
When calculating how much water to add, weigh each component, and multiply by the percentage of water content you need. Again, every glaze is different –clay content, modifiers, and even certain colorants factor into this. So you’ll have to add water, adjust as needed, and record that % for later reference.
Let’s say that you want to start with 50% water, take the 825 gram example and multiply by 50%:
825 x 0.50 = 412.5
412.5 can translate to cubic centimeters (cc), milliliters, or grams, depending on how you wish to measure it out. I use a graduated cylinder (ml) or large syringe (cc).
50% water will probably not be enough, but it’s better to err on that side, as you can always add more water.
A crystalline glaze contains little to no clay and usually a large amount of fritted or calcined components. If you add only water to it, it will soon settle like fine sand, and be extremely difficult to work with. When applied to your work, it will crack, peel, and flake off during drying. This is why suspenders and binders are added.
Gum Water Solutions :
In the case of the above recipe, 1% Bentonite or CMC is listed (1% is offered as a rough figure only). Either must be thoroughly mixed with the other dry ingredients before water is added, or it will form irregular clumps. I prefer to mix them into water before hand. You can buy pre-mixed “gels” from commercial suppliers, but it’s hard to know how much of what you will be adding, so I like to make my own. Take note that if your glaze recipe has a large enough clay content, then additives like these are likely unnecessary, and can result in a gummy mess.
I had heard about pre-mixing CMC, etc into water through potters such as Jeff Zamek. But it didn’t sink in just how simple and effective it could be until John Tilton and I visited our friend Kris Friedrich at his studio. I have since kept premixed & hydrated forms of many ingredients in air tight containers, ready for use.
Using CMC as an example then, I often add 0.5-2.0 grams of dry CMC powder per every 8oz of water. The amount of CMC necessary will depend upon what type of CMC you have. Some CMC will actually contain larger particle wood pulp as a filler, whereas certain “food grade” varieties are so powerful that the 0.5gCMC : 8ozH2O ratio is enough.
Blend the powder into warm water until mixed, let it sit for an hour or so (or preferably overnight), and blend again before use. This pre-hydrated gum solution can then be mixed with the dry glaze batch to produce a usable consistency (52-72% of the dry glaze weight works well in my crystalline bases).
Include the weight of all additions (colorants, etc.) and round the decimal.
825 grams of dry ingredients X 0.55 = 453.75 (round to 454) cc/ml of gum solution.
I mix the dry glaze ingredients and gum solution in a blender until it’s uniform, and then pass the glaze through a 80-100 mesh sieve. One trick is to add the water to the glaze and let it sit for a 1/2 hour or so. It will mix faster and go much easier on your blender.
Some CMC’s are infused with a fungicide. This prevents it from decomposing and losing it’s strength. Many crystalline artists agree that keeping their glazes for long periods of time has bad consequences; however, if you choose to do so, simply add 0.02% Copper Carbonate to the gum solution when mixing it up. This will deter organic growth and at that level, it won’t discolor even white/clear glazes.
Lastly, I suggest weighing the hydrated glaze to obtain a specific gravity. By doing this, you can adjust the glaze if, e.g., it loses water during storage. If the specific gravity is off, your viscosity will more than likely change as well, and you can easily add too much or too little glaze during later applications, skewing the results.