Butane vs. Propane: Which is Hotter?

Q: Looking on the charts, at “total heating value after oxidation,” propane is 19768 BTU/lb. and butane is 19494 BTU/lb., but in every other category butane looks hotter. Which is really going to heat my jewelry items faster?

What is a Glaze?

Q: What is a glaze?

A: In plain terms, a glaze is a very thin layer of glass formed on a clay pot during the firing processes, that is, during one of the times that the fragile clay vessel is heated to a high temperature (above 1800° F, 1000° C).

Are Glass and Glaze the Same?

Q: Are glass and glaze the same?

A: Sometimes, but not often. Glass itself dates back at least 50 centuries. Mix sand and some other dry minerals, heat in a fireplace, and you obtain a material often called a “network polymer” (a “mer” is a unit molecule and “poly” means many, joined together).

What Affects a Glaze Surface?

Q: What affects a glaze surface?

A: A glaze surface may be glossy, satiny, or rough (dry matt); the actual result will revolve around the silicon oxide and the alumina oxide contents, both in relative and absolute terms. A glass that contains 60% silicon oxide (silica, flint, quartz), plus or minus 5%, will usually make a good glaze.

How Many Materials are there in a Glaze?

Q: How many materials are there in a glaze?

A: If one examines many glaze recipes, one soon realizes that most of them contain ten ingredients, or less. These, in turn, are used repeatedly in different recipes for a given firing range (low-fire, mid-fire, or high—fire).

What Factors Go Into a Glaze?

Q: What factors go into a glaze?

A: Glaze design is both simple and complex; the list of basic oxides can be expressed in simple chemical terms, but the interaction of the usual ingredients (up to 10) is most difficult to describe and even more difficult to predict with confidence.

How Do You Design a New Glaze?

Q: How do you design a new glaze?

A: It may sound like magic but to design a new glaze successfully requires no mysterious chants, just a thorough understanding the factors involved in the process. There are two main ways to develop a new glaze:

  1. Choose suitable raw materials (mostly those that have worked before) and mix them in various proportions to meet a planned series of glaze tests; or
  2. Choose an appropriate “formula”, based on previous experiments, and derive a “mix-batch” recipe for testing, etc.

What is a Seger/Unity Formula?

Q: What is a Seger/Unity formula?

A: One way to help evaluate a glaze recipe is through the Seger or Unity Formula named after Hermann Seger who a century ago arranged glaze components into a particular order. He called one group the “flux” oxides—usually the oxides of Lithium, Sodium, Potassium, Magnesium, Calcium, Strontium, Barium and sometimes Iron.

What’s New in Glaze Design?

Q: What’s new in glaze design?

A: With the advent of the home computer, doing a glaze design no longer involves lengthy, tedious calculations by hand. Nowadays, any potter can undertake glaze design providing she/he has:

  1. Access to a microcomputer, either an IBM type with a disk operating system (DOS) or an Apple “Macintosh” type with its “pull-down” menus; and
  2. Access to specialized computer programs that simplify glaze calculation and analysis.

Bust in Clay

Q: I want to make a life-sized bust in ceramic clay and fire it. Are there any special precautions I have to take?

Cast Concrete Sculpture

Q: How do you go about making concrete sculpture like the kind you can buy for your garden?

Surface Treatments for Ceramics

Q: I’m making some ceramic sculpture and I don’t want to glaze it, I want to treat the surfaces differently. What can I do?

Clay vs. Slip

Q: What is the difference between slip and clay? Can I make slip just by adding water to clay?

Clay Dust

Q: My studio is piled with scraps of dry pottery clay, and it seems really dusty in there. Is this going to give me lung cancer? What can I do about it?

Clays for Sculpture

Q: I want to try doing sculpture. What kind of clay should I use?

Forton MG Plaster

Q: What is this Forton MG plaster you mentioned, and where do you get it?

Gas, Electric, or Wood Kilns

Q: My new place in Washington State has a brick barbecue, which I plan to use for a wood-fired kiln. But the place also has heavy electricity and natural gas. Which is better for ceramics, a wood kiln, a gas kiln, or an electric kiln?

Handbuilding Ceramic Sculpture

Q: How do you make armatures for handbuilding ceramic sculpture?

Cheapest Mold Material for Clay Models

Q: I’m making models in clay that have lots of undercuts, and would like to take molds of them so I can make permanent sculptures in plaster or polyester resin. What is the cheapest thing I can use that won’t tear up the originals too badly?

Raku Pottery

Q: What is Raku, and how do you do it?

Smooth Surfaces in Plastiline Clay

Q: I want to make a small sculpture in plastiline (oil-based) clay. I want to create extremely smooth flowing curves, with no tooling marks. What is the best way to achieve this result?

Making Clay Pipes

Q: I want to make some clay pipes for smoking. What clays are best for resisting heat? How do you get that long tunnel to go down the stem? And how do you sculpt on them without mashing them up?

Faience—Egyptian Paste

Q: I’ve gotten curious about Faience, and I want to try it out. Do I need a special kiln? What is it best for, and what special treatment do I give it?

Making Stamps for Ceramic

Q: Does anyone know how to make stamps for ceramic?

Plastiline Clay

Q: What is plastiline clay and how can I mix my own?

Making Figures with Polymer Clay (Sculpy)

Q: I want to make some figures in Sculpy. Can I use a wire armature, and if so, what gauge is best? Can I add new clay to a part that’s been baked? And will it take paint?

Controlling a Kiln

Q: What can I do to control the temperature of my kiln and make it more like an oven?

The Oil Clay FAQ—Oil-based Clay for Sculpture

Andrew Werby discusses various oil-based modeling clays and their use, with notes on modeling technique, as well as several recipes for mixing ones own. This article covers the following topics: origins and qualities, available varieties, armatures, tooling, smoothing, mixing ones own, variations, safety considerations, and clean-up.

The Clay FAQ—Water-based Potter’s Clay and its use in Sculpture

Andrew Werby tells how ordinary water-based clay can be used to create permanent fired sculpture, as well as its use for making models for production in other materials. This article covers the following topics: clay defined, direct and indirect use, waste molds, natural clay, reusing clay, handworking clay, plaster and clay, joining clay forms, firing, slipcasting, making slip, modifying clay bodies, building hollow forms, freeze/thaw problems, armatures, accelerated drying, and surface treatments.