Making ceramic glazes from scratch involves combining three core ingredients (silica, alumina, and flux) with water, then adjusting the mixture until it coats your work evenly. The process is straightforward once you understand what each ingredient does and how to measure consistency. Whether you’re working with a published recipe or developing your own, the fundamentals are the same.
The Three Ingredients Every Glaze Needs
Every ceramic glaze, from a simple clear to a complex crystalline, is built from the same three components. Silica is the glass-former. It melts and creates the smooth, glassy surface you see on finished pottery. Alumina acts as a stabilizer, helping the glaze “shrink to fit” the clay body underneath so it doesn’t run off during firing. Flux lowers the melting point of everything else, because silica alone would need temperatures far beyond what most kilns can reach.
You rarely add these three components as pure chemicals. Instead, you use minerals and compounds that contain them in combination. Feldspar, for example, contributes silica, alumina, and a small amount of flux all at once. Ball clay and kaolin supply both silica and alumina. This overlap means that changing one ingredient in a recipe shifts multiple variables at the same time, which is why glaze development involves a lot of testing.
Flux Changes With Temperature
The type of flux you need depends on your firing range. Low-fire glazes (typically cone 06 to cone 1) use materials like borax, commercial frits, and gerstley borate to melt at lower temperatures. High-fire glazes (cone 6 to cone 10) rely on whiting (calcium carbonate), dolomite, bone ash, barium carbonate, and even wood ash. Feldspar pulls double duty at high temperatures, acting as both a glass-former and a mild flux. Using a high-fire flux in a low-fire recipe won’t produce a glassy surface, and using a low-fire flux at stoneware temperatures can cause the glaze to run right off your pot.
Starting With a Proven Recipe
If you’re mixing glazes for the first time, start with a published recipe rather than inventing your own. Ceramics textbooks, community studio glaze logs, and online databases all offer tested formulas with known results. A recipe will list dry ingredients by weight, usually in grams or as percentages that add up to 100. Colorants and other additions like iron oxide, cobalt carbonate, or tin oxide are listed separately as a percentage added on top of the base recipe.
Weigh each ingredient on a gram scale. Accuracy matters here. A few grams off on a small test batch can shift the result noticeably. Combine the dry ingredients in a clean bucket, then slowly add water while stirring. The amount of water isn’t usually specified in the recipe because it depends on how you’re applying the glaze (dipping, brushing, or spraying each require slightly different consistency). A good starting point is roughly equal parts water and dry material by weight, then adjusting from there.
Getting the Consistency Right
The single most useful skill in glaze mixing is learning to measure specific gravity, which tells you the ratio of glaze material to water in your bucket. The method is simple: fill a container with exactly 300 milliliters of your mixed glaze, weigh it in grams, and divide by 300. Since water weighs exactly 1 gram per milliliter, pure water gives you a specific gravity of 1.0. A typical dipping glaze falls between 1.45 and 1.50.
Different glazes have different sweet spots. A black matte glaze, for instance, might need to be exactly 1.44 to avoid being too thick or too thin. As you work with a particular recipe, you’ll learn its ideal number. Write it down. Specific gravity is the most reliable way to get repeatable results, because eyeballing thickness or dipping a finger in the bucket leaves too much room for error. If your glaze is too thick, add water in small amounts and re-measure. If it’s too thin (usually from evaporation and topping off with too much water), let it settle, pour off some water from the top, and stir again.
Once mixed, pass the glaze through an 80-mesh sieve to break up lumps and catch any unmixed material. Sieving twice is common practice. Let the glaze sit overnight before using it, as some materials need time to fully hydrate.
Why Frits Exist
Some raw glaze materials are either soluble in water (meaning they dissolve and migrate unevenly through the glaze layer) or hazardous in their raw form. Frits solve both problems. A frit is a pre-melted glass that has been cooled and ground into a powder. The manufacturer has already combined flux materials like boron or lead with silica at high temperature, locking them into an insoluble, much safer glass matrix.
Lead glazes illustrate why this matters. Raw lead compounds were the standard low-fire flux for centuries, and over 400 cases of lead poisoning were documented among British potters in a single year in 1897. Lead frits dramatically reduced poisoning rates because the lead is chemically bound into the glass structure, making it far harder to inhale or absorb. Most modern potters avoid lead entirely, but frits remain essential for incorporating boron and other soluble flux materials into low-fire glazes without the handling risks of raw chemicals.
Avoiding Crazing and Shivering
The two most common glaze defects are crazing and shivering, and they’re opposite sides of the same problem: a mismatch between how much the glaze expands and contracts compared to the clay body underneath.
Crazing looks like a fine network of cracks across the glaze surface, sometimes visible right out of the kiln, sometimes appearing days or weeks later. It happens when the glaze contracts more than the clay as the piece cools, stretching the glaze like pulling a size 5 sweater over a size 6 frame. The glaze cracks to relieve that tension. Shivering is the reverse: the glaze is under too much compression and flakes off at edges and rims, sometimes sending small sharp chips of glass flying.
The fix for both problems is adjusting the thermal expansion of the glaze to better match the clay. For crazing, you need to lower the glaze’s expansion. Substituting some of the high-expansion flux (like sodium) with a lower-expansion option (like magnesium oxide) is one effective approach. Band-aid fixes like firing higher or applying thinner coats might mask the issue temporarily, but the root cause is always the expansion mismatch. The only reliable solution is changing the glaze chemistry or switching to a clay body that’s more compatible.
Crazing can also develop long after firing if the clay body was underfired. Porous clay absorbs moisture over time, which causes it to expand slightly. That slow expansion stretches the glaze from underneath, eventually producing cracks even in a glaze that looked perfect coming out of the kiln.
Protecting Yourself While Mixing
Dry glaze materials are the biggest health concern in ceramics. Many contain silica dust, which causes permanent lung damage with repeated exposure, and some contain toxic metals like barium, manganese, cobalt, or chromium. The most important precaution is keeping materials out of the air you breathe.
Wear a respirator rated for fine particulates whenever you handle dry powders. A basic dust mask is better than nothing, but a properly fitted respirator with the right filters offers real protection. Work in a space with good ventilation, ideally with an exhaust fan pulling air away from your face. Wet-mop floors and surfaces rather than sweeping, which just kicks dust back into the air.
One of the simplest safety measures is buying glazes already mixed into a wet slurry rather than as dry powder, which eliminates the riskiest part of the process entirely. If you do work with dry materials, wear nitrile gloves (especially if you’re sensitive to nickel or copper, both common in glaze ingredients), and wash your hands thoroughly before eating or drinking. Keep food and drinks out of your studio space entirely.
During kiln firing, wear goggles with infrared-blocking lenses when looking through the peephole. The intense infrared radiation inside a hot kiln can damage your eyes and contribute to cataracts over time.
Testing Before Committing
Never glaze a finished piece with an untested recipe. Make small test tiles from the same clay body you’ll use for your work, and fire them in the same kiln at the same temperature. A glaze that looks perfect on porcelain may craze on stoneware. A glaze that melts beautifully at cone 6 in one kiln may be underfired in another with a different heating pattern.
When developing your own recipes, change one variable at a time. If you adjust both the silica and the flux in the same test, you won’t know which change caused the result. Keep a notebook with the exact recipe, application method, clay body, and firing schedule for every test tile. Glaze development is slow, methodical work, but a well-documented set of tests will teach you more about how glazes behave than any book can.