How to Make Glaze Tests

Make 5-10 test tiles


  1. Roll out a large slab no thinner than 3/8, up to 1/2 " thick.
  2. Cut out 4 x 6" tiles. Optional: make 5 extra for yourself to keep.
  3. Make a shallow groove about 1 1/2" up from the bottom, across the tile to catch the glaze if it runs. If the groove is too deep the tile will crack. The tiles will be fired vertically.
  4. Divide the upper part of the tile into three horizontal bands by making band of texture across the middle 1/3.
  5. You may also add a band of white or dark slip.
  6. Dry the tiles between layers of newspaper, and turn occasionally, to prevent them from curling up at the corners.

Make your 4" x 6" test tiles look like this:


Brush or dip glaze over smooth area, texture, and colorant lines.

thin glaze . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . thick glaze

-----------------------------------

texture band

-----------------------------------
optional band of white / dark slip


___ Red Iron Oxide Line ___
___ Copper Carb. Line ___
___ Cobalt Carb. Line ____

Incise a groove across the tile about 1 1/2" up from bottom. Leave this space unglazed

To prepare test batch of glazes

  • Wear an approved dust mask or respirator.
  • Bring one container with snap-on lid for each test you will do.
  • Label each container with its contents.

Prepare your clean bisqued tiles with colorant lines.

If the tiles are dusty, they may be rinsed in water and allowed to dry. Then draw one thin horizontal line in each of the 3 coloring oxide solutions provided*, across the tile just above the groove.

*2 recipes for oxide writing/decorating solution:

  1. 1 tsp. colorant + 1 tsp. Gerstley Borate/Frit #3124.
  2. 75% Frit #3124 + 25% colorant, + 1Tbsp liquid laundry starch.

Weigh out the ingredients in your recipe. Leave the dry material containers in their order on the counter. Do not take them to another table.

TIP: To make 3 tests of the same base more accurate and less time consuming, line up 3 containers and weigh the 1st ingredient 3 times, then the 2nd 3 times, etc.

Weigh out glazes very carefully. Check off each amount as you weigh it, because the oxides look alike and you can easily loose track of what you are doing.

If you spill, use a wet sponge to clean up.

Dry mix and then add water to each test. When all tests are weighed out, very carefully dry mix each. Spilling will create an inaccurate test.

Slowly add water and mix to a thick paste. Then add water by teaspoons until the glaze is the consistency of thin yogurt.

Apply the glaze to the test tile. Brush a thin coating on the left side, and a thick coat on the right. Do not drag the oxide colors into the glaze. The two areas should touch so that the entire surface of the upper portion is covered. Wipe off any excess glaze from the edges.

Label the back of the tile with red iron oxide. Regular ink will burn away, so write the glaze name and entire formula clearly on the back with a red iron oxide solution. Use a fine brush and make sure the solution looks about like India ink; if it's too light it won't show.