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PC-70 Copper Red: Tips and Tricks

Amaco PC-70 Copper Red is a dramatic, lovely glaze, based on ancient East Asian copper red ware. Copper Red can be tricky, but I’m bringing you my best tips to get the best results.

How it works

When a copper glaze is fired in a reduction atmosphere, depriving the firing of oxygen, the normally green copper oxide turns a deep oxblood red. Reduction firing normally cannot be done in electric kilns, but the formulation of PC-70 Copper Red creates a reduction atmosphere inside the glaze, creating a true reduction copper red glaze without the need for a reduction kiln firing. 

1 coat PC-70 Copper Red

Application

Because the thickness of the glaze application affects the amount of reduction occurring, the glaze must be applied generously. Too thin an application will not create enough reduction and will give less than optimal results.






2 coats PC-70 Copper Red


Apply Copper Red directly from the jar without thinning. The glaze is thick to make it possible to build a sufficiently thick application with 3 coats. Use a thick, natural fiber fan or hake brush to apply 3 or more even coats, allowing each coat to dry completely before applying the next. The dry, raw glaze should be at least 1.3 mm thick before firing. If your results are clear or patchy, the application is too thin or not applied evenly. Applying more glaze and refiring will not help, since the reduction materials will have already burned off.



3 coats PC-70 Copper Red




We suggest that you create a test tile with 3, 4, and 5 coat sections and fire before using it on a final piece.








Firing

Copper Red is at its most red when fired to cone 5. Firing to cone 6 will give a more purple-red effect, as well as increase the potential for running. We recommend using witness cones to verify that your firing is reaching the target temperature.

PC-70 Copper Red fired to cone 5















PC-70 Copper Red fired to cone 6















Clay Body

PC-70 Copper Red on Sibelco Black Stoneware 2002

Since Copper Red breaks clear on edges and pronounced texture, your clay will show. We mostly show Copper Red on white clay. Brown or buff clays will show up as brown and can make the red look muddy in contrast. Historically, copper red glazes were used on porcelain or white clays, for a bright contrast between the glaze and clay, but Copper Red can also be beautiful and dramatic on black clays. Test on your chosen clay before applying to a final piece.







PC-70 Copper Red on Aardvark's Coleman Porcelain, fired to cone 5



We’ve found that some clay bodies will react with Copper Red in a way that creates a frosty blue glaze, instead of the deep oxblood red. Clays that we are aware can create this effect are:

Aardvark Coleman Porcelain

Sibelco Atelier-Masse Wiesse (Studio White Clay)

Sibelco Black Stoneware 2002

This list is not exhaustive and may be updated as we receive new information.

We recommend using Amaco A-Mix White Stoneware (11M) for the results seen on our website.



PC-21 Arctic Blue (2 coats) over PC-70 Copper Red (2 coats), fired to cone 6 on A-Mix White Stoneware

Extra information:

Some users have applied a single coat of a clear glaze over Copper Red, which can help keep the reduction enclosed, but our testing shows a sufficient application is

still required. Layering Copper Red with other glazes may not be successful and may increase running even as it reduces the red result. Shown is 2 coats PC-21 Arctic Blue over 2 coats PC-70 Copper Red, fired to cone 6 on A-Mix White Stoneware.

Related glazes:

PC-71 Flambe, DL-70 Oxblood, and PC-72 Fire & Ice are all formulated similarly to PC-70 Copper Red, and the situations described in the tips and tricks are also relevant to those glazes.

Happy Glazing!