Easily account for shrinkage of clay slabs by using a scanner and photo-editing app to size up templates. This is especially useful for custom projects where finished size is critical. 

My light switch covers were born from a mix of nostalgia for the funky switch covers I had in my bedroom as a kid and from being stuck at home for over a year, staring at my walls and realizing how much I hated beige plastic light switch plates. 

I spent a good amount of time troubleshooting the process, and have come up with a pretty reliable method to scale up any type of light switch cover using a scanner and photo-editing app. I avoid warping of the clay slabs by using parchment paper and drywall boards in the rolling and template-cutting process. Here is my method.

Shrinkage of Your Clay Body

Make a shrinkage ruler to calculate the shrinkage of your clay body by rolling out a small slab to the same thickness as the project you will make, then carefully measure using a ruler and mark a line that is 4 in. (10 cm) in length onto the slab. After firing to your final temperature, compare the clay ruler to the standard ruler and determine the shrinkage rate. If your clay ruler measures 3½ inches (9 cm) total, you will know that your clay shrinkage is 10% (each 1-cm mark would represent 10% shrinkage).

Wavy nerikomi light switch cover with red and white clay bodies. Photo: Zoe Prinds-Flash.

Make Your Template 

Scan the light switch cover you plan to replace, then scale up the scanned image in an editing app (like Adobe Illustrator, Affinity Design, etc.) to account for the shrinkage rate. If your shrinkage rate is 10%, multiply the dimensions by 1.10. This new number will be your template switch dimensions (if you are familiar with image editing programs, you can also scale the image up by 10%. Alternately, if your scanner  has scaling capabilities, you can let it do the math for you and set it to scale up 10%). If you’re not completely certain of your shrinkage rate, repeat this scaling-up process with a few rates to test out each one. Print and cut out your template. 

Note: It’s important to make sure that the document you’re editing is formatted to be 8½×11 inches, so that it doesn’t get resized in the printing process. You’ll want to be mindful of your print settings as well. Make sure it’s printing at 100% scale.

1 Scanned light switch cover templates scaled up 10% to account for shrinkage post-firing.

Form Your Slabs on Drywall Board

Roll out your slab on a drywall board. If you’re using a slab roller, measure the thickness of the board, then add ¼ inch to that, and set your roller to that height. Place the canvas on top of the drywall board, place your clay on top of the canvas, then place your second canvas on top of the clay, and send it through the slab roller. 

Slowly peel back the top canvas, being careful not to warp the slab, and smooth the surface of the clay with a rubber kidney-shaped rib. Place a piece of parchment paper on top of the smoothed clay surface, then place a drywall board over that. The paper will move with the clay over the drywall board as it dries and shrinks, helping to prevent it from sticking and cracking. 

Flip the drywall-board-and-clay sandwich over, then remove the original drywall board (now on the top of the sandwich). Carefully remove the canvas and smooth the surface of the clay. Place the drywall board back on the clay to make a drywall/clay sandwich with the parchment side facing down, and cover with plastic. Let the clay stiffen to leather hard. This should be a slow process to avoid warping, especially if your switch covers have combined clay bodies (like marbled clays, inlaid colored clay, or nerikomi). I like to flip the drywall/clay sandwich periodically to encourage even drying throughout the slab. 

2 Covering a freshly rolled and smoothed slab with parchment paper and a flat drywall board. 3 Flip the drywall boards with the slab in between so that the parchment paper is on the bottom of your clay slab. Carefully peel back the canvas and smooth the newly exposed slab surface.

Trace the Stencil and Cut the Slabs

With the parchment-paper side on the bottom, remove the top layer of drywall and use your template to cut the switch-cover shapes and the interior areas to accommodate screws and the light switch. Be careful not to lift or deform the clay slab as you cut. The stenciled slabs should remain flat for this entire process. 

Compress the edges of the holes you made for the screws and the light switch to prevent hairline cracking in those areas as it dries. Carefully remove excess clay around the covers and compress/smooth the edges. Finally, cover with the drywall board and slowly dry under plastic. 

4 Tracing the scaled-up switch cover templates onto a leather-hard clay slab.

Touch Up and Fire

I use a green kitchen scouring pad to sand the dry greenware light switch covers. Be sure to wear a respirator and do this in a well-ventilated area. You can apply underglaze at this point if you’d like. Then, bisque fire your switch covers. 

After the bisque firing, decorate your covers as you wish and finish by glaze firing.

5 Covering the switch covers with a drywall board while they get bone dry. 6 Sanding greenware with a scouring pad. Photo: Nina Perkins.


Purchase 1-inch switch cover screws to accommodate the thickness of the clay cover. I like to paint the screws with nail polish to match the switch cover design. You may need to sand or file down the edges of your rectangular switch hole (I find it helpful to make that opening slightly smaller rather than larger if I’m worried about not getting it spot on. If it’s bigger, it can look a little funny when installed, but if it’s slightly smaller you can file it to size so it fits properly). 

You may need to angle your screws in a particular way so that they fit in the pre-drilled holes of the light switch. The metal surrounding the screw holes on the light switch expands if you put a bit of muscle behind the screwdriver. 

the author Katie Cameron creates under the moniker “cry baby clay” In addition to making hand-built and wheel-thrown ceramic items, she also owns and operates a pottery studio in Minneapolis of the same name. It is a hybrid personal studio and community clay resource. Her intention is to help minimize barriers associated with working with clay. For more information, visit www.crybabyclay.com