The original purpose of a glaze on pottery was to seal the pot, making it a more effective container, especially of liquid, and consequently making it much more useful in cooking. Pottery was being slip coated and painted as early as 3500BC but fired glazes of lead and tin were not being used until around 1200BC.

The largest technological influence on glazing has probably been the availability of increasing numbers of impurities to affect the appearance of the finished work. Contemporary glazing is primarily a decorative finish, although the commonest substance for construction of receptacles for liquid, particularly hot liquid is undoubtedly ceramic and will be glazed.

Glazing is an interesting art because the final stage of production transforms the bland into the beautiful, and the artist just has to know that is what is going to happen. Many times they don't, and the finished product has been strangely affected by unplanned environmental states in the kiln. Put it down to experience and start again - hopefully you know what the difference was and can repeat it if you like the effect. Commercial pottery naturally uses more controllable kilns, while artists often prefer outdoor ovens fired by wood or gas.

As well as being affected by the temperature and oxygen levels, the colour and texture of the finished glaze is affected by the combination of minerals included and the clay foundation. Glazes incorporating feldspar, lead and salt are typically clear, with tin resulting in an opaque white. More recently (13th century), copper might be induced to produce blue-green and red colours, or dolomite to give brown and blue hues. Modern artisans have a bewildering array of combinations in their arsenal.

The robustness of glazed pottery accounts for an enormous quantity of knowledge we have about ancient civilisations because it has frequently lasted for thousands of years, even without burial and archeological excavation.

Glazes can be really pretty decorations, and if your ceramic piece has a lot of flaws in it the right glaze can take your attention away from the flaws and put it back on the glaze. There are some basic things you need to know about glazes. Glazing takes two steps:

  1. formulate base
  2. add colorant

Three Basic Components (chemical table)

  1. Glass former (XO2) X being a variable
  2. Flux (XO, X2O)
  3. Refractory (X2O3)

A glass former is the part of a glaze that is glassy, the most common glass former in a glaze is Kaolin, though Potash Feldspar also has glass former properties since most ingredients do more than one thing.

A flux is a chemical that is added to a glaze to lower the temperature at which it matures. Common fluxes are Potash Feldspar and Gerstley Borate.

A refractory is the part of the glaze that keeps things from melting too much, and keeps it all from dripping off your masterpiece. Most common refractory is Gerstley Borate.

A common Basic Glaze base would be:

  • Four Parts Kaolin (Al2O3, 2SiO2, 2H2O)
  • Three Parts Potash Feldspar (K2O, Al2O3, SiO2)
  • Three Parts Gerstley Borate (2CaO, 3B2O3, 5 H2O)

Most chemicals fall under the chemical chart above, but there are some exceptions. One exception is that 3B2O3 is also a flux even though it's chemical composition lends itself to only a refractory.

To make an actual glaze with color is a little more complicated. A glaze recipe that we were given in class is this:

Delanie's Red/Brown

  • F-4 soda Feldspar 20.2gm
  • Silica 30.22gm
  • EPK 3.96gm
  • Gerstley Borate 31.89gm
  • Talc 13.91gm

This is the recipe without the iron which gives it the color or the water. Once you have the dry ingredients mixed, add a couple of grams of iron, and then add water. This recipe makes 100 grams and can be doubled or quadrupled easily. The amount of water varies since water just suspends the chemicals so that they can be coated on the ceramic piece evenly, and since bisqued ceramic pieces absorb a lot of water it works out evenly. The water should be enough that it seems to dissolve when stirred (but please note that it will not actually dissolve since the chemicals cannot be water soluble since it would no longer be a glaze because the chemicals would be absorbed into the clay instead of being suspended topically). You also don’t want to add too much water since this will dilute the glaze.

When creating a glaze, you will want to do a whole series of test tiles, make sure to number them and mark each subtle change you make on paper. This technique is called a line blend, and it's where you take a glaze and add something slowly to it, note this doesn’t form new glazes, it just adjusts one you like.

some Terminology:

  • Feldspar-Potash, cone f4 feldspar is not changeable with soda ash.
  • Craze-Crackling when you want it, crazing when you didn't plan on it, it's when the glaze is too small for the clay and it has to crack to try to sit evenly, This is a defect
  • Shivering-This is the opposite of crazing, this is when the glaze is too heavy, too big, and it pops off. This is also a defect
  • Coefficient of Expansion-When things expand and contract together, the higher the coefficient the more crazing you might/will get.
  • Frit-Companies take chemicals that are normally water soluble, chemicals like lead and boran that are hazardous to our health if ingested and they fire them with silica and grind it to a powder, this process makes the chemicals safer to use since they are no longer water soluble and will not leech out of the glaze after firing.
  • Fusion Point-The point when the glaze melts.
  • Vitreous-When it's solid, the maturing point of glaze. The optimum density.
  • Interface-Where the glaze and the clay body meet, where they fuse.
  • Oxide-Naturally occurring colorants:
  • Stain-Commercially made oxides that you can use straight, they are dependable, but they are also expensive.
  • Glaze-Glassy coat that can add color and strength to the clay and also makes it non-porous
  • Refractory-Heat resistant, keeps things from flowing.
  • Flux-Lowers the melting point
  • Volitalization-When certain chemicals go airborne, this especially happens in reduction kilns and raku fires; copper is one of the most volatile. To stop this from happening don’t fire copper glazes with sensitive (white esp.) glazes.
  • Opacifier-Something that makes the glaze opaque, a chemical like zinc.
  • Bentonite-Gummy, it's a suspension agent, you add it to your liquid glazes to keep the chemicals from settling. Interestingly this is the main ingredient in cat litter, and you should be able to get it at health food stores for cheap.
  • Eutectic-Singly the chemicals will not melt, but together it lowers the melting temperature.

Ceramics is fun, and I would suggest anyone take a class in it at their school, it can also be done at home as an expensive but rewarding hobby.

All info gleaned from my ceramics class in school. For more info look online.

In baking, as above, "glaze" generally refers to a smooth, glossy finish.

Painting bread dough with a bit of beaten egg (also called an egg wash) will result in a browner, shiny crust (as in challah).

Most often, a glaze is essentially a thinned-down frosting. This comes in handy when you're in a hurry or find yourself with a cookie or cake which is a little underwhelming in flavor, or simply undersweetened. I'm a fan of tart desserts, but occasionally I've overdone it with the lime juice in cookies and ended up with something too intense, but rescuable with a sugar glaze to balance the flavor.

Some recipes fancy it up with a bit of butter or flavoring extract, but almost all glazes simply consist of powdered sugar whisked with enough water, milk, or fruit juice to create a workable consistency. Leave it a little thick if you want to smear it on cookies, thinner if you want it to drip down the sides of a Bundt cake.

I have never tried it, but I feel like an almond cake with an orange or grapefruit glaze would be stupendous.

Glaze (glAz), v. t. [imp. & p. p. Glazed (glAzd); p. pr. & vb. n. Glazing.] [OE. glasen, glazen, fr. glas. See Glass.]


To furnish (a window, a house, a sash, a case, etc.) with glass.

Two cabinets daintily paved, richly handed, and glazed with crystalline glass.


To incrust, cover, or overlay with a thin surface, consisting of, or resembling, glass; as, to glaze earthenware; hence, to render smooth, glasslike, or glossy; as, to glaze paper, gunpowder, and the like.

Sorrow's eye glazed with blinding tears.

3. (Paint.)

To apply thinly a transparent or semitransparent color to (another color), to modify the effect.


© Webster 1913

Glaze, v. i.

To become glazed of glassy.


© Webster 1913

Glaze, n.


The vitreous coating of pottery or porcelain; anything used as a coating or color in glazing. See Glaze, v. t., 3. Ure.

2. (Cookery)

Broth reduced by boiling to a gelatinous paste, and spread thinly over braised dishes.


A glazing oven. See Glost oven.


© Webster 1913

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