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All About Pottery Glazes

You can buy these glazes in any pottery or ceramic shop.
Crystalline glazes are the most fun to coat your pottery with because of all the different shapes that come out when it is fired.
Some of the large crystals grown in a glaze even look like flowers, and sometimes they often resemble lichens and three dimensional fans and feathers as shown in the picture below.

Crystalline glazes are those in which the oxides in them melt and form into new and different patterns and as the glaze cools it looks like glass with crystals inside. A bunch of crystals too small to be seen individually will give you opacity and matt surfaces. Larger crystals can be grown upwards of six inches, appearing to float in a glassy background. The wonderful shapes, of distinct and different color from their background are the result of trial and error mixing of the glaze formula and the cooling rate of the kiln. They call it science and patience, we call it "look what we got with this mixture", and the beauty shows itself magically from the process. If you are experimenting on your own it is very important to keep notes on ingredients and amounts that you mix together and firing and pausing times on the kiln.

Crystal shapes are soft flat rounds which may collide with each other in clusters, changing their forms. Usually a central star or bundle of needles can be seen in a smooth area before a fibrous looking ring fans out like a halo. Further haloes edge the shape where it meets the background glaze.This shape is colored by the penetration of a coloring oxide into the crystal and is clearly seen against the background. There is often a delicate fringe of a slightly different color where crystal meets the background glaze. The haloes can be placed centrally or around the border of the crystal. Where the glaze is thicker, as in the well of a bowl, the three dimensional forms can be seen as fibrous fans filling the depth. Time is needed during the cooling of the glaze for crystals to form.

In the early stages of cooling, if the temperature is held around 1800 degrees F for about two hours, the crystals begin as simple needle shapes. These can fan out at each end into double axe head like shapes. These attractive and fascinating crystals can be frozen at this stage by cooling the kiln rapidly after this growing period. The fuller rounder shapes develop when the temperature is maintained for further crystal growing periods. These pauses are programmed into the cooling cycle of the kiln controller and may last from three to eight hours.

Porcelain is often the choice of body for use with crystalline glazes, because bright colors show up well and there is little contamination from the body during the slow cooling. The main glaze ingredient is a frit. This provides most of the glass which melts at the appropriate temperature.

Frit Formulas Commonly Used

Ferro Frit

Ferro Frit

High Alkaline Frit

This complex crystal above shows the fan-like growth and three dimensional appearance in the depth of glaze. The blue staining of the crystal is incomplete due to the small percentage of cobalt oxide in the recipe. The pot was glazed first with a Ferro Frit based glaze and over this, a High alkaline Frit base glaze. Each one contained 0.5% cobalt oxide and 3% manganese carbonate.

In order to color premature zinc silicate crystals, the coloring oxides must be able to fit into the lattice structure. To enter the crystal, the metal coloring substance must be able to occupy one of the six sites otherwise held by zinc in the zinc silicate lattice. Cobalt, nickel, copper, iron and manganese are transition metals and are adjacent to zinc in the periodic table. Their substance sizes are also similar to that of zinc. Therefore all these metals can enter and color the crystals.

The colors here are from ilmenite and cerium oxide which has properties similar to tin oxide.

This fringe edged crystal is approximately 1 1/2 inches across. It appears in a glaze with 1.5% vanadium oxide and 1.5% ilmenite in a Ferro Frit base glaze. This glaze shows how copper oxide can give a green stain to both crystal and glaze. The glaze has 3% copper oxide and 3% barium carbonate. The barium carbonate shifts the color towards turquoise.

Glazes are brushed on, thicker above than below to allow for considerable glaze movement. Calcining the zinc oxide removes water and helps to avoid flaking of the glaze. A binder is used to make the glaze less brittle. Every pot is fired on a catcher made to fit the piece. Surplus run off glaze is contained by the catcher which must be separated after firing. The glaze and foot are then ground smooth. This is a complicated process requiring specialized grinders for the particular shapes.

These glazes make your pottery kind of one of a kind because no two pieces will be the same. I like to give them for presents, and the people that receive them really enjoy them also. What I like best of all is opening the kiln to see what I got!! These glazes are the neatest and most fun of all.

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Have you ever come up with a good idea while working with your handmade pottery or ceramics and thought that you would like to share it with others? You have? Well, why not send it to us and we will add it to the tips page for all to see.

Handmade pottery can be a very gratifying hobby that produces fun and satisfying results. For many people it's an enjoyable release that is created by working an inanimate mound of clay into a beautiful work of art that you made through your artistic abilities.

The best way of starting out is to take a few lessons. You will probably waste quite a bit in materials when you first get started. Figuring out how to truly make handmade pottery correctly and shape into what you want it to be can be quite an ordeal. The different tools that a normal shop will have can be fun to try. You will soon see which ones you like to use the most and then when you are ready you will know which ones to buy.

When you get all set up, just enjoy the hobby and have fun at it. Some people get pretty serious and start selling their creations at craft fairs and small stores, but others just like to create items for themselves, relatives, and friends. Whichever kind of handmade pottery you desire to endeavor, enjoy the hobby and have fun doing it.