Cutting Straight Edges and Working Off a Template
Okay, so you've got an even slab now, rolled and rested and covered while you weren't looking at it. This lesson is where that slab turns into an actual piece instead of just a nice flat rectangle you're proud of for no reason.
Cutting straight, and cutting to a shape you planned instead of a shape you happened to end up with, is the difference between a box that closes right and a box that looks like it's apologizing for itself.
Start with the template, not the clay
Before you touch your slab, cut your shape out of paper or thin cardboard first. Cereal box cardboard is genuinely fine. I know that sounds like I'm underselling it, and I am, on purpose, because people get precious about this step and buy acetate sheets and stencil kits before they've even made one box. Don't. A cereal box and a pencil will get you through your first ten projects.
Measure twice. Actually measure twice. If your box needs a bottom and four walls, figure out those dimensions on paper, including a little extra on the walls for trimming later, before you cut anything from clay you can't get back.
This is also where Wyatt's slab roller comes into the story, a little sideways. Before I owned a real one, he built me one out of two dowels and a cutting board, because he's the kind of person who'd rather build a tool than watch me struggle without one. It was genuinely terrible. The dowels weren't quite the same diameter, so my slabs came out with a faint taper no matter what I did, and I compensated by trimming more off one side than the other every single time. I used it for a year anyway, because he was so proud of it, and also because it taught me something useful: you can work around an imperfect tool if you know exactly what it's doing wrong. Templates are the same idea. Once you've measured and cut one on paper, you know exactly what you're aiming for, and any drift in the clay becomes obvious instead of mysterious.
Cutting the clay
Lay your template on the slab while the clay is still soft-ish, not leather-hard yet. You want it easy to cut but firm enough to hold a clean edge.
Use a needle tool or a knife, held straight up and down, not angled. An angled cut gives you a beveled edge, which sounds fancy and mostly just makes your joins harder later because the surfaces don't meet flush. Go slow. Let the tool do the work instead of dragging the clay.
Cut just outside your template line, not exactly on it. Give yourself a hair of margin. You can always trim more off; you can't put clay back once it's gone.
Straight edges are not the same as perfect edges
Here's the thing. "Straight" here means the edge is clean and true enough to join well, not that it's machine-perfect. I'll say the unpopular thing again because I believe it: don't chase symmetry. If your rectangle is a sixteenth of an inch off-square, that is not the crisis your brain is telling you it is. What actually matters is whether the edges are clean enough to score and slip and seal properly. A slightly imperfect box that's structurally sound will outlast a "perfect" one with sloppy joins every time.
Where precision does matter is at the corners and any edge that's going to meet another edge. Those need to be true, because a gap there is where cracks start in the kiln. Check them against your template again before you set the piece aside.
Working the edges before they dry
Once you've cut, clean up the cut edge with your fingertip or a damp sponge, just enough to knock off any burr or ragged bit. Don't oversmooth it, you're not trying to erase the fact that it was cut, you're just making sure it's not going to snag or crumble when you handle it later.
Cover your cut pieces immediately if you're not assembling right away. You already know this one, I've said it before and I'll keep saying it: our air here is dry enough that a slab can skin over faster than you'd think possible, and a skinned edge won't join cleanly no matter how carefully you scored it.
A word on the knife or needle tool itself. Keep your fingers behind the blade, not alongside it, and don't cut toward your other hand. It's a small tool and it's easy to get casual with, which is exactly when people nick themselves.
Before next time
Cut out at least two paper templates for a simple box shape, even if you don't touch clay again before our next session. Getting comfortable measuring and planning on paper is half the battle, and it'll save you from wasting a good slab guessing.
~erin