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A standard shape and size of glaze test is important to be able to compare one test with another, especially over time (so that old tests look the same as new ones)
Joe Schmidt, lab technician at
Plainsman Clays, developed the glaze testing cone, it is very practical. It is a standard shape and size that is always used, this serves well for comparison and documentation purposes.
They are easy to make.
They are easy to photograph
They are stable and less likely to tip over and break
They stack well in boxes
They display a glaze in a way that is akin to a piece of pottery or ceramic.
Steps to make these:
Print the pattern and cut it out
clay to 1/4 inch (6mm) thickness Cut the shape out of the clay using the pattern
Apply a band of slip to one end and attach the other using a 15mm (1/2 inch overlap)
Press the joint firmly together (use a stick on the inside to support) and press the indentations
Dry the clay to leather hardness and carve a design on the side opposite the join (to show what it does on edges, in varying thickness around contours and on an uneven surface)
Stamp the identification of the clay at the bottom
Dry the testers carefully to avoid cracking
Use a knife to trim off any sharp edges
When dipping these in glaze consider the following:
Dip down to within 15mm (1/2 inch) of the base
Label clearly on the bare clay section
Dip the top half again for a double-thickness.
Use the link below to download the pattern file.
An example of the value of a good glaze testing sample.
These are made at
Plainsman Clays in Alberta, Canada.
Preparing to make a glaze testing cone: cutting around the pattern
In this picture a piece of cardboard is used as a template, you can download a pattern using the URL link on this page.
Making a glaze testing cone: applying the slip for the join.
A viscous slip will make a better join and minimize the chance of water-splits developing at the edge of the overlap.
Making a glaze testing cone: finishing the join.
With most clays no scoring is needed, the slip and pressure are enough to make a good join.
Making a glaze testing cone: Incising the surface
Glaze thickness thins on the edges of the incised lines and thickens at their bases. This enables variegating glazes to showcase their visual effect with varying thickness. And these test the ability of opaque glazes to still cover well when the layer is thin.
Making a glaze testing cone: Stamping an identification.
The code numbers get recorded with the pictures in our testing system (an account at