There is a certain mystique that goes with mixing your own glazes, and much of that mystique is earned. To mix your own glazes means that you are well and truly delving into the area of inorganic chemistry.
But wait! There is more to it than simply chemical formulas! The materials we use are not pure scientific chemicals. Not only that, but you can't dump them willy-nilly into a bucket and expect great results!
Mixing pottery glazes takes knowledge. Knowledge of the components themselves, and knowledge about how best to put them together.
Glazes are made up of a few basic types of components:
- Silica -- it is silica that forms the glass
- Alumina -- a refractory and stiffener, this allows the glass to stick to vertical and even overhanging surfaces while it is molten. It is what makes glass into glaze.
- Fluxes -- these make the silica melt at a lower temperature than it would otherwise.
- Colorants -- As you might expect, these add color to the glaze
- Modifiers -- These are ingredients that can change the glaze in some other manner, such as opacifiers, those that add opalescence, those that encourage crystal growth, and so on.
Glaze Components in Ceramic Materials
The reality of glaze ingredients is not as easy as looking around a chemistry lab for pure chemicals. The most basic glaze ingredients come in combination forms; for example, alumina and silica are found in every type of clay as well as rocks such as feldspars. On the other hand, many colorants and modifiers are sold to potters by their chemical name or formula; for example red iron oxide, Fe203, is one of the most commonly used ceramic colorants.
If you want to understand more about ceramic ingredients, especially if you are interesting in coming up with your own unique recipes, I strongly recommend you study Clay and Glazes for the Potter.
If you are new to raw glaze ingredients and mixing your own glazes, stick with using recipes from other potters. Creating a new glaze is not for the beginner. (It is not worth the cost of kiln shelves, or even a new kiln, to go at it without a good theoretical and practical grounding, first.)
Ceramic recipes abound, including those for clay bodies, glazes, slips, and so on. Most recipes these days are formulated so that the combined weight of the components equals one hundred (as in, 100%). This makes it much, much easier to create batch weights that match your own needs, from a (dry) two hundred pound batch of a clay body to ten kilos of dry glaze. For more, see How to Read and Use Glaze Recipes.
Glaze Mixing Tools, Etc.When mixing glazes, you need to take into account:
- Dust Control: The work space needs excellent dust control. In addition, you should always wear lung protection. A dust mask is simply not enough. I strongly recommend you use a dual-cartridge respirator.
- Wash Up: You need a sink with a special trap system or wash-up buckets. Remember that many ceramic ingredients should not be washed down the drain.
- Water: glazes should be mixed using distilled water only.
- Three or More Buckets: Make sure they have air-tight lids.
- Scales: All measurements are by weight. You will need an accurate scale that can handle the amount of weight.
- Skin Protection: Use latex gloves.
- Sieve: A large sieve or screen.
- Mixer: More on this below.
Mixers for Glazes
Although a lot of us use our gloved hands or a large kitchen whisk, there are tools out there that make mixing glazes a lot easier and faster. These are attachments that can go on a normal hand-held drill.
Potters have two choices of mixer drill attachments. The first are the ones made especially for mixing glazes. These are more expensive, but tend to be designed to both reduce air being added to the liquid glaze and to handle the density of the glaze.
The second choice are the paint mixers (also called paint stirrer attachments). These are cheaper, may be easier to find, and do the job. They will, however, be more likely to add some air into the liquid glaze (which effects application).
How to Measure Glaze Ingredients
Be sure to have latex gloves on before you begin handling raw glaze ingredients. Some of them can enter the body through the skin or through cuts.
Unless you are working on a tiny glaze batch, you will need a scale that can handle several pounds or kilos of weight. Scales may be mechanical, such as a triple-beam balance scale, or they may be digital. In many (if not most) ways, the digital scales are easier to use. All good scales, however, tend to be fairly expensive.
Always measure your ingredient in a scoop or container, not loose on the scale. Make certain to tare the scale, whether physically or digitally, so the weight of the container is subtracted.
Prepare to Mix the Glaze
This may seem awfully straight-forward, but like mixing baking ingredients, it isn't quite as foolproof as one may think. You cannot, if you want good results, just dump the ingredients into a bucket of water and stir.
With respirator and gloves on, first sieve all measured dry ingredients together, similar to sifting flour and baking powder together. It is easiest to measure and dump ingredients into one (dry) bucket, then sieve them into a second dry bucket.
How Much Water?
Once you have the dry ingredients measured and sieved, it is time to get them wet! Proportions of water to the dry batch weight will change due to humidity, how the glaze is to be applied, and the needs of the glaze itself. (Some glazes work best when thinner than average or thicker than average.)
In general, for a dry batch weight equaling 20 pounds, I begin with about 2 gallons of distilled water in a 5 gallon bucket. (Remember that it is easier to add water than take it out!) The final consistency for most dipping glazes will be like that of heavy cream. If you want more precise control, you can use a hydrometer and determine your own preferred specific gravity for your glazes.
How to Mix the Glaze
Slowly sprinkle the dry ingredients into the glaze bucket, while at the same time stirring up the water either with your gloved hand, a whisk, or a mixer drill attachment. The trick here is to get every particle wet but without introducing any air into the water / liquid glaze.
Keep the mixer attachment, whisk, or hand fully submerged while it is rotating. If using your hand, break up any lumps you feel. With the whisk and mixer attachment, move the blades so as to mix all areas.
Once the Glaze Is Mixed
After you have thoroughly mixed the glaze and gotten rid of any large lumps, it is a good idea to sieve the liquid glaze to find and break up any small lumps. To do this, slowly pour the glaze from the mixing bucket into another bucket, with the glaze pouring through the sieve.
I suggest letting the glaze rest for about fifteen minutes before using it. This allows any air to rise to the top and escape, as well as giving all the particles a chance to become thorough;y wet.
Remember glazes settle. Some settle more rapidly than others (in which case a suspending agent is often added to the ingredient list). If it has been longer than a few minutes since you have used the glaze, stir it up again with a long stir stick or the mixer attachment.
Storing the Glaze Batch
Glazes should be stored in air-tight containers that won't easily open by accident if the container gets knocked over. Always label glazes by name. Keep all glaze containers out of reach of children, pets, and wildlife.
If you use up your batches quickly, you should not have too much trouble with the glaze ingredients settling into a concrete-like sediment on the bottom of the bucket. However, if you are storing glaze for longer than a few days, do shake or stir them up thoroughly every few days.
If, for some reason, you are decanting the glaze into several smaller containers (such as sharing it with potter friends), be sure that all particles are fully mixed and in suspension. Label all the containers and note any hazardous material.