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Week 19

  1. In order to understand the composition of glaze materials it is useful to be able to reference the chemical symbol for each material. Some materials are even more complex. Cornwall stone, for instance contains all of the components to form a complete glaze on its own. The potassium (K2O).. .serves as the flux. the alumina (Al2O3) is the stabilizer, and there are eight molecules of silica (SiO2) serving as the glass-former. What is the chemical formula for Cornwall stone?

    1. KO.AlO.SiO

    2. K2O.Al2O3.8SiO2

    3. K2O.Al2O3.SiO2

    4. none of the above

  2. Tin Oxide, Titanium dioxide, and Zironium oxide are in a group of glaze materials that are know as ___________.

    1. fluxes

    2. coloring oxides

    3. suspension agents

    4. opacifiers

  3. ______________can be very useful at middle and high-temperature ranges. It can have a profound effect on glaze color, particularly with iron (dulls color), copper (increases brilliance of color), chrome (browns out color), and tin (changes the color to pink or brown). At higher percentages it is an opacifier. It can also cause crawling and pinholing.

    1. Zinc

    2. Strontium

    3. Barium

    4. Magnesium

  4. APT-II and Blue Lace Mender are ___________________ commerical glaze additives that cn be used for a variety of applications including suspending glaze in the bucket, extending brushability, and hardening the unfired glaze surface.

    1. Wax resists

    2. Epsom Salts

    3. Flocculants

    4. Acrylic emulsions

This weeks questions come from text in The Ceramic Glaze Handbook, Mark Burleson, Revised Edition , English translation c. 2003, Lark Books, a division of Sterling Publishing Co, Inc.

Note from Pres: Hoping these are quick and easy, this book was purchased for the formulas, but at the same time there is excellent material explaining glaze chemistry.

 

 

Answers:

  1. 2. K2O.Al2O3.8SiO2-In order to understand the composition of glaze materials it is useful to be able to reference the chemical symbol for each material. The chemical symbol is and abbreviated set of letters and numbers that identifies the elements present in each material and the number of atoms or molecules of each. For instance, a molecule of silica (S2O3) is composed of two atoms of silicon and three atoms of oxygen. Some materials are even more complex. Cornwall stone, for instance, contains the components needed to forma a complete glaze on its own. The potassium (K2O) in this naturally occurring material serves as the flux, and the alumina (Al2O3) is the stabilizer, and ther are eight (8) molecules of silica (SiO2) which serve as the glass former.

  2. 4. Opacifiers-paciï¬ers Opacifiers are materials that contain compounds such as tin, zirconium, and titanium. They are added to a glaze to decrease its transparency or make it more opaque. The addition of these materials will whiten the glaze base.

  3. 1. Zinc-Zinc oxide ZnO Zinc oxide is useful as a glaze flux in the middle and higher-temperature ranges. It can have a profound effect on glaze color, particularly in combination with iron (dulls color), copper (increases brilliance of color), chrome (browns out color), and tin (changes the color to pink or brown). The effects become more dramatic at higher temperatures. It is also known to cause glaze problems such as crawling or pinholing.

4. Acrylic emulsions-Acrylic emulsions are commercial glaze additives that can be used for a variety of applications including suspending glaze in the bucket, extending brushability, and hardening the unï¬red glaze surface. They are sold commercially as APT-II, Blue Lace Mender, and other names.          

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Hopefully someone can help me understand why the answer to question 1 is K2O.Al2O3.8SiO2 when Digital Fire indicates that Cornwall Stone contains other molecules that aren't in this formula.   Thanks for the help!  -S. Dean

 

Cornwall Stone

Alternate Names: Cornish Stone, China Stone, Corn Stn, China-stone

Oxide Analysis Formula

CaO 1.81% 0.240

MgO 0.14% 0.026

K2O 4.30% 0.339

Na2O 3.30% 0.395

TiO2 0.15% 0.014

Al2O3 16.33% 1.189

SiO2 73.76% 9.117

Fe2O3 0.20% 0.009

 

Oxide Weight 742.81

Formula Weight 742.81

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Not one that I can answer that well. However, I do not believe that materials consider trace elements in the Chemical representation.

 

 

best,

Pres

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