Liz Denys

Clay shrinks as it dries and even more as it's fired, so it's useful to have a way to estimate the final size of in-progress work - especially if you're making multiples or trying to fit pieces together. One way to do this is with shrinkage rulers. I figured I'd design my own shrinkage rulers and provide a way for folks to make them themselves since ceramic tool costs can add up.

To make your shrinkage rulers:

1. Download the shrinkage ruler set you need:
   • colorful set for letter size paper
   • black and white set for letter size paper
   • colorful set for A4 size paper
   • black and white set for A4 size paper
2. Print at 100% size. (These files are all 400 dpi.)
3. Verify that the 0% shrinkage standard ruler at the top matches the size of an existing regular ruler you have. This quick calibration step will make sure nothing got out of scale during printing!
4. Cut out your rulers.
5. Optionally, laminate or cover in packing tape to help them last longer.

To use your shrinkage rulers:

1. If you're using commercial clay, look up how much your clay is estimated to shrink. If you're using a blend of clays or custom clays, you'll have to calculate how much your clay shrinks. An easy way to do this is measure the length of a wet piece right after you form them and again after it's been through its glaze firing. You can then calculate the estimated shrinkage rate:
   
2. Pick the shrinkage ruler that corresponds to your clay's shrinkage rate. If you're between shrinkage rates, you can estimate with a nearby size. Remember that shrinkage rates are estimates, and a piece's actual shrinkage depends on many variables, including how wet your clay is and how close it is to it's original composition (this can change with repeated recycling).
3. Measure your wet piece with the shrinkage ruler! The length shown is the expected length your piece's dimension will be when fired.

The fine print:

1. Reminder that shrinkage rulers only give estimated lengths!
2. You're welcome to print these shrinkage rulers for yourself or your business. You may use the printed shrinkage rulers privately, even in commercial applications (I hope they help your ceramic art and business!), provided you do not redistribute or resell the shrinkage rulers themselves in any form, digital or physical.

I'm continuing my clay body reviews series with two very heavily grogged "sculpture" clays I've used.

Note that I currently practice in a community studio that glaze fires to cone 6 in oxidation, so my observations reflect that.

Standard 420 Sculpture:

• Cone 6: average shrinkage 8.0%, absorption 1.5%
• Light straw when fired to cone 6: more yellow/beige than most white stonewares so the color is something to consider in your final vision (or engobe in something else)
• So much grog that it's best described as working with wet sand, non-derogatory
• I've made complicated open coil-based structures with this clay that have been formed across many studio sessions over a couple days, and they've survived without cracking! Wet clay attaches readily to leather hard and even slightly dry clay. Wrapping my works in dry cleaning bags until done and dry before bisque was enough - I was worried I'd have to make a damp box, but not with this clay!
• The grog is white and grey, and it comes in a variety of sizes, including some that is visually rather large. The grog really shows if you sand to smooth the surface. I typically dislike how this looks - the result ends up looking more like concrete than clay.
• If you use this for functional ware or anything you move around a lot, you'll certainly want to sand the bottom since the groggy surface is extra rough to protect tables and counters. Burnishing alone doesn't usually make this clay smooth.
• Can be thrown when very soft, but your hands will feel scratched if you're not used to it!
• Angled slab joins join readily, and support coils press in quickly and easily.
• Some members of my studio prefer to make plates with this clay because the high level of grog significantly reduces warping. I personally prefer to make plates with clays with far less grog that I dry very slowly. High palpable grog content means a weaker object, and I prefer more strength in objects that are handled frequently.
• Can be marbled with 798, but needs to dry slowly.

Standard 798 Black Sculpture:

• Cone 6: average shrinkage 10%, absorption 1.0%
• Dark brown when wet, fires to a gorgeous black at cone 6 when unglazed.
• Clear glazes will make this clay look brown, so you need to use a black like Coyote Black or Amaco Obsidian to preserve the black color if you want to glaze it.
• So much grog that it's best described as working with wet sand, non-derogatory.
• The grog is white, and provides a lovely contrast when on the surface or sanded to be revealed.
• Like 420, you'll probably want to sand the bottom of anything you'll pick up and put down more than once.
• Very similar working qualities to 420 - a true joy for handbuilding!
• Can be marbled with 420, but needs to dry slowly.

Starlit sky on a clear night / the milky way / eternity / clarity / raindrops sticking to window glass
Black stoneware clay with fine white grog, slab-built, denim satin glaze

Blue jeans / well worn leather / rows of cornflowers along a dirt path
Medium brown stoneware clay with white grog, slab-built, denim satin glaze

Bauhaus design / negative space / boundaries that are clear on paper
Tan stoneware clay with black speckles and light grog, slab-built, glossy yellow, glossy orange, and matte turquoise glazes