GLAZE

Mrs. Murphy … Mrs. Murphy When can I color my project? What are my choices? And Why do we say glazing and not painting?

The use of glazes is familiar in many everyday articles, FOR EXAMPLE….

Glaze vocabulary: 1.What is glaze? 2.What ingredients make up a glaze? 3. How is a glaze different from an engobe? A layer of glass that makes your pot colorful, shiny and food safe. Silica : tiny particles of glass Alumina : “glaze inhibitor” that keeps the glaze from running Flux : brings down the melting point of silica Pigment : color Engobes contain less flux, so the silica particles don’t melt completely.

4. What kind of glaze do we use? 5. What types of low-fire glaze do we have? Low fire glaze. It melts the silica within the glaze at 1800 degrees/Cone 06. Very predictable. Overglaze: color and the shine all in one glaze (needs 3 coats) Crystal glaze: overglaze with a base color and colored speckles Underglaze: color, but no shine in the glaze. Shine comes from clear overglaze applied later. Stain: pure pigment. Painted on, then wiped off. Makes texture stand out.

Terms used to describe glazes: 6. Transparent: 7. Opaque: 8. Glossy: 9. Satin: 10. Matte: 11. Semi-_____: 12. Food-safe : can see through it solid and not see through shiny partial shine no shine at all (not food safe) Partially, or a little bit _____ Safe to eat or drink out of

Ceramic Glaze: is the process of coating a bisque piece with a thin layer of a glassy material.

The Egyptians invented the first glaze using cobalt and copper. A Quartz Frit press molded dish. Decorated with black slip drawing c.1450 BC.

Modeled figurine of a hippopotamus in Blue Quartz Frit Paste. Probably made about 1400 BC. in the 18th Dynasty of the New Kingdom (or Empire) period in Egypt.

Glazes are most often a mix of dolomite, frit, silica/flint, feldspar, sodium borate, clay and whiting plus metal oxides or carbonates. The chemicals are mixed with water.

WHY glaze your work? Glazing is functionally important for vessels and decorative ware, which would otherwise be unsuitable for holding liquids due to porosity. In addition to the functional aspect of glazes, aesthetic concerns include a pleasing surface effect. Glazes may also enhance an underlying inscribed, carved or painted design.

WHY GLAZE? 1. Functionally Important for holding liquids. 2. Aesthetics (the look)

Glazing Vocabulary – Colorful Clay Bisque – Clay that has been fired once, unglazed. Bisque firing – The first firing of a clay to drive out chemically combined water and carbonaceous materials prior to glazing Cone – a time-temperature indicator of heat work in a kiln usually symbolized with a Kiln – pronounced “KILL” is a furnace for calcining or firing ceramic products.

Many variations of glazes are possible: clear, glossy, matt, colored, & textured glazes.

Glaze recipes are carefully formulated to melt at appropriate temperatures and produced a surface with desired characteristics.

Colors The colors available will depend upon the firing temperature (low or high fire), & the chemistry of the glaze.

The Art Classroom Will offer two types of glazes: LOW FIRE: Cone 06 =1800F AND HIGH FIRE: Cone 5 = (2185F)

LOW FIRE CONE 06 = 1850 degrees

HIGH FIRE GLAZES CONE 5 = 2185 degrees

HIGH FIRE GLAZES CONE 10 = 2400 degrees

Glaze Application The glaze materials are usually applied as a water- based suspension by Spraying, Brushing, Pouring, and Dipping methods.

With all glazed items, a small part of the item (usually on the bottom) must be left unglazed, or else it will stick to shelf during the glaze firing.

Ouch! What would happen to that glaze grade!?!

STEPS TO GLAZING 1.Sponge the piece to clean the surface. 2.Stir/Mix the glaze. 3.Apply the glaze. 4.Clean the ¼” bottom edge AND base of the piece.

After applying a glaze, the piece is glaze fired, which is a hotter firing than the bisque. This is the final firing of the 6 clay stages.

The powdered coating melts into a glass-like coating, turning into your shinny finished piece.

Firing of Ceramic Glazes Conventional glazes are not fired below 950°F and may be fired as high as 3000°F depending on the application in question. In most cases, oxidation conditions are used but for certain products reduction conditions are required.

OVER GLAZES: Decoration applied on top of a layer of glaze, is referred to as over glaze. Over glazes include applying one or more layers or coats of stain over a glaze on a piece of pottery or by applying a non-glaze substance such as enamel or metals over a glaze.

Oxide Stains: to be applied over a glaze or as a matt decoration alone. 1. Cobalt 2. Copper 3. Iron 4. Manganese

Decoration applied under the glaze on pottery, is generally referred to as underglaze or slip. Pigments are applied to the surface of the pottery piece in the greenware / leatherhard state. After the pot has been bisque fired then the wet glaze is applied over the slip decoration. The pigment fuses with the glaze, and appears to be under a layer of clear or colored glaze. An example of underglaze decoration is the well known "blue and white" porcelain produced in China and Japan. The striking blue color is achieved by using a cobalt pigment, fired at the correct temperature. Slips, Under Glazes

Glazing Facts: Glazes MUST be thoroughly mixed before and while using to keep the chemicals from separating. No more than three layers of glaze should be applied in any one spot on a piece. Be sure glaze brushes are clean and dry before and after use. Water can thin glaze, another color can contaminate glazes. Glazes are identified by a name and code number. Glazes Cone Numbers must match the Cone Number of the clay being used or they will not stick. (We use Cone for each – White Art, Low Fire Clay). If glazes are applied properly, brush strokes should disappear. BEWARE!!! Glazes rarely come out of clothes. Never pick up a jar by the lid, nor shake them. Open away from your body, preferably over a sink, to be safe. Glazes are not the color in the bottle they are when fired. The DO NOT mix like paints. You can layer glazes but the result is always a mystery.

Three consistencies of glaze: Transparent – You can see through the glaze when fire if applied properly. This would be the glaze you would use over the under glaze. It must be applied in a DABBING motion not a brushing motion or you will loosen all the under glaze design below. It will not be clear in color when you apply it. Translucent – You can partially see through the glaze when fired if applied properly. Opaque – You will not be able to see through the glaze when fired if applied properly.

Steps in glazing: 1.Pot must be bisque fired first! 2.Wash dust off 3.Get one bottle of glaxze and take it back to your seat 4.Paint 3 solid coats of glaze on all surfaces except the bottom 5.Put glazed pot on the cart by the door for firing 6.Put glaze back on shelf, wash all brushes/cups

Glazing Tips Wipe off or Rinse your ceramic work first Be sure to shake/stir the glazes Glaze inside first Using a paint brush, paint on 2-3 coats on Make sure to leave a “Dry Foot” ---Clean Bottom and leave 1/8” clean from the bottom of the sides!!!

Glazing Tips continued: Only get one bottle at a time. Make sure lid is on before you shake! Wash brush before you use it! Wash brush after you have finished and put up. Label in your sketchbook the glaze you used and where it was used.

HELPFUL HINTS… 1.3 is a magic number 2.Less is more 3.Wipe your bottom

Glaze Basics Glazing Safety: Read the label! Some glazes are toxic in liquid and dry form before first firing. Read the label again! Some glazes are not food-safe or dinnerware-safe. Never put these on bowls plates etc. Never eat while glazing. Wash your hands thoroughly when finished.

Finishing: Check to be certain you have accurately recorded all of the glazes you have used. Clean glaze bottles and secure lid evenly. Return glazes to shelves. Wipe down table surfaces well. Wash out brushes in cold water and return to holder with the bristles up. Wash your hands well. Final Words: Please take good care of these glazes and do not waste them; they are expensive.