Notes on cone 6 clay bodies, part 2

July 4, 2024

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.
The raw clay is straw colored and slightly textured, and there is a bit of orange-toned flashing at the glaze line
Standard 420's straw color shows in the unglazed section of this planter's drip tray, and there's also some flashing from the glaze near the edges.
The sanded sections reveal the various grogs in the clay.
I sanded the base of this piece so the slightly rough surface of Standard 420 wouldn't scratch tables, and you can see the contrast between the sanded bottom (outside) layer where the varied grogs are revealed and the rougher surfaces of the other layers where they are still covered by clay particles.
Coiled sculptural elements of a fully fired and glazed planter - some left raw unglazed textural black, some glazes in a blue satin glaze
This handbuilt planter was made of Standard 798 over multiple studio sessions. The sculptural coil structures attached readily with my regular slip and score process, and it dried evenly enough to not crack with my regular process of drying under a single plastic dry-cleaning bag.
Coiled elements of a wall sculpture in the greenware phase
This coiled wall art piece was made out of equal parts Standard 112 and Standard 420 wedged fully together. There's still ample grog in this hybrid clay body to work the same as the Standard 798 planter's coiled structure.

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.