Tips and Tools: Standing Test Tiles Don Clark

Appears in the April 2020 issue of Ceramics Monthly.

Test tiles provide essential information for fired ceramic pieces, but can be a hassle to keep organized in and out of the kiln. This pair of DIY tile stands addresses numerous problems.

I do a lot of glaze testing and needed to find solutions to the problems of moving and handling large quantities of test tiles through the different stages of glazing and firing. This starts with deciding the test tile that best suits your needs: small pots, thrown rings cut into sections, shards, or reject pots. Each type has its benefits and disadvantages from making to storage, and I have tried them all.

Finding a Solution

The approach to test tiles that works best for me originated with Ron Roy. I studied with him in Toronto, Canada, in the late 1970s, and I believe that Ron still teaches this method in his glaze workshops. Ron uses flat test tiles and fires them in soft firebricks with parallel slots cut into them. The tiles stand vertically in the slots, allowing each brick to efficiently hold multiple tiles. This is a DIY equivalent of a tile crank.

These sitters can be made from new bricks, salvaged bricks, and broken pieces of bricks to create a range of sizes. Using a set square and a pencil, mark the slots, then paint the areas to be removed with iron oxide (see 1, 2). A standard 4×9-inch soft brick can fit 4 long slots measuring ³⁄₈–½ inch wide (cut lengthwise) or 8–9 shorter slots measuring 1/2 inch (cut across the width). I have an old saw dedicated for cutting brick, as the refractory material will ruin the teeth of a saw over time. Make the cuts for each slot approximately 1 inch deep (2). Then with a flat-head screwdriver and a hammer, gently tap the cut section until it pops out (3). I level and smooth the base of the groove with a file. Test with one of the tiles to ensure there will be a good fit. Caution: Always wear a dust mask and work in a well-ventilated area when carving and sanding soft firebrick.

The size of the test tiles used depends on your personal preference. I make my test tiles 1½ inches wide by 4 inches tall and ¼ inch thick, as well as 4 inches wide by 4 inches tall by ¼ inch thick (measured in the raw state). A full firebrick can hold up to 18 of the 1½-inch-wide tiles. Make no mistake, a small tile of this size will reveal a lot of information about a glaze. When I find something interesting, I continue testing on the larger tiles.

Load the glazed test tiles onto the tile sitters and then place the bricks around ware in the kiln or have entire shelves of test tiles placed in sitters. Care must be taken at this stage, as the bricks will leave debris if moved along a kiln shelf. Firebrick, once fired, becomes brittle and will leave refractory crumbs behind. I use a small, handheld vacuum to tidy up around the bricks once I have placed them in the kiln.

There are several advantages to this method of firing test tiles. When a glaze test gets overfired and runs, it runs onto the brick and not the shelf. The test tiles are easily separated from the bricks post firing, generally with little damage to the bricks. This method also solved the problem of firing a large volume of tiles at one time.

Handling the Tiles

Glazing, moving, and storing the tiles on the racks resulted in refractory brick debris on work surfaces, which wasn’t desirable in my small studio where I have my throwing and glazing areas.

I devised a simple solution to replace the use of firebricks in my glazing area. Using some pine shelving, I cut, glued, and nailed nominal ¾×¾-inch pieces of the pine to 1×10-inch pine boards (4). The spacing between the added strips of wood is determined by fitting a bisque tile (about ³⁄₈ inch), thus allowing an adequate space for the tiles. I place the freshly glazed tiles on these tile racks prior to firing. This is also a convenient way to store the tiles until the next firing. As my gas kiln is in the back garden of my house, I now have a safe and efficient way of carrying the tiles to the kiln. A 15-inch long board can hold as many as 60 of the 1½-inch test tiles. Once at the kiln, I transfer the tiles to the fire-brick sitters (5) and place them in the kiln.

Post firing, back in my workshop, I use the wooden racks to hold the fired tiles while I examine and record the results (6). This flat tile format stores easily. The glaze-fired tiles can be kept on the wooden racks for reference, or they can be removed and easily stored in a shoebox. (I can fit 200 or more tiles into an old shoebox).

the author Don Clark is a potter working in cone-10 reduction-fired porcelain. He apprenticed for both Ron Roy and Kayo O’Young in Toronto in the 1970s, and currently lives and works in Millbrook, Ontario, Canada. To learn more, find Don on Instagram @drclark42 or contact him atdrclark42@gmail.com .