Tuesday, February 21, 2012

Glazing 101

I'm going over glazing with my students this week, and rather than just winging it and trying to remember everything I want to say, I decided to write out a handout for them to refer to. If anyone else is teaching beginner ceramics and finds this useful, feel free to copy it or alter it in any way that's helpful to you and your students.

I'm hoping that a more thorough understanding of glazing procedure will result in less disappointments for new students because of glazing mistakes. Although the disc grinder can be kinda fun to use;)

I tried using wax resist on one of my pots to get a clean line of separation between my two glazes. Unfortunately, I dried the blue glaze with a heat gun before wiping it off the resist areas, and the wax melted, so those beads of blue glaze are there to stay. Oh well, we'll see what it looks like after firing. Maybe I'll like it and start doing it on purpose!
Drawing over glaze with black underglaze. This underglaze is Duncan's Concepts brand, so I think it has a little flux in it. It gets a bit shiny at cone 04, but I know it survives midfire. I've never put it over a glaze before, so I'm curious to see what happens.

Here's the handout, hope someone else finds it useful!

Glazing 101

Greenware vs. Bisqueware
  •             Greenware is work before it has been fired in the kiln.
  •             Bisqueware is work that has been fired once to a lower temperature than glaze firing, and       is ready to be glazed and fired. We only glaze fire work that has been bisqued.

Underglaze vs. Glaze
  •             Underglazes are ceramic paint colors that can be used for surface decoration on either   greenware or bisqueware. They generally do not get glossy when fired in the kiln.             Underglazes may be coated with a clear glaze to seal them onto your work, and make a piece food safe and water tight. Underglaze colors may change dramatically under a clear glaze. Read all labels before use.
  •             Glazes are suspensions of glass, flux, and clay that melt in the kiln  to become a glassy coating for your work. They are used on bisqueware only in this studio. Glazes can be purely decorative, or they can make your work safe to eat and drink out of. What you see is not what you get! For example, a glaze that looks red before firing may turn deep blue afterwards. We use cone 5-6 glazes in this studio, not cone 05. There is a huge difference in that zero!

Glazes available at BGCW - AMACO and studio mixes
  •             AMACO glazes - commercially prepared glazes from AMACO ceramic supply             company. Beech Grove Clay Works offers several of these free for student use, and carries additional glazes available for student purchase.
  •             Studio glazes are custom created and mixed here in the studio by the artist in residence.        These need to be thoroughly mixed before each use, as the contents tend to settle.

Glazing your work
  •             Use fine grade sandpaper to remove rough spots and sharp edges.
  •             Always wipe your piece with a damp cloth or sponge before glazing to remove dust and      oils that may act as a resist and cause your glaze to not adhere well to your pot.
  •             Use wax resist to keep glaze off the bottom of your pot. Glaze can and will stick to the       kiln shelf, damaging the shelf and your pot. Use a sponge brush and wax resist in the jar, or use the hotplate to dip your foot in wax. If you get wax on your pot where it is not wanted, bisque fire the piece again to remove the wax. Wax resist cannot be washed off.
  •             Dipping/pouring glazes - large buckets of glaze - Always mix glazes well before each use. Use a wire whisk or the hand drill with a mixer attachment. Be sure all contents on the bottom of the bucket have been thoroughly mixed into the glaze before using. Dip your piece for 3 seconds, then remove for good glaze coverage. Wipe the bottom of your pot with a damp cloth or sponge after dipping to remove residual glaze. Remove unwanted glaze with a sharp tool first, then wipe the remaining glaze with a damp sponge.
  •             Brushing glazes - small jars of glaze - always read instructions on commercial glazes.             Most AMACO glazes require 2-3 brush coats for good coverage. Allow each coat to dry       thoroughly before adding another. Gum solution may be added to improve brushability,   but be careful. Adding too much may cause your glaze to dry slowly.

Glaze testing and experimentation
  •             Clay body - glazes may look different on different types of clay
  •             Layering - Different effects can be achieved by layering  2 or more glazes on your pot.      Take notes! You will not remember what you did to get that effect, so write down what glazes your put on your pots. Do not apply brushing glazes over a layer of dipped glaze, as the top layer tends to flake and crack off.
  •             Thickness of application - how thick the glaze is applied will affect your results. Very thin coverage may give a completely different color than you expect. Be careful of  applying your glaze too thick, as glaze can drip or run off the pot onto the kiln shelf. If your glaze has cracks in it after it dries, it is probably too thick. These cracks may result   in bare spots after firing.
  •             Textured glazes - glazes that break or change color over a textured surface. Look best on            work that has been stamped, carved, or textured in some way. Keep this in mind when making work. Textured effects can often be achieved by layering glazes.


Hobby Potter said...

I'm interested to see how that black underglaze works as well. I've been trying to figure out how to make the fine lines and everything I try ends of blurring ( except an underglaze pencil which doesn't work too well over glazes). Please share after it's fires :) !

Lori Leaumont said...

I will! So far, I get the nicest lines using underglaze on greenware, and then firing on a translucent or clear later. I have a friend who does a lot of majolica, though, and he gets great surfaces. I'll have to ask him what he uses, but you can see his work here: http://www.flickr.com/photos/funland/

Thanks for commenting!

Hirsita Dixit said...
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