Reinforcing with Coils and Blending Seams
Okay, so we've got joins now. Score and slip, moisture matched on both sides, walls that actually want to stay together. That's the foundation. This lesson is about making those joins stronger than they need to be, because "strong enough" is a bet, and I'd rather not bet on a piece I've spent three sessions building.
Here's the thing. A scored-and-slipped join is a good join. But on anything with real height, or a wide base meeting a wall at close to a right angle, or a piece that's going to get picked up and handled a lot, I want more insurance than slip alone gives me. That's where coils come in, not as decoration, as structure.
Why a coil instead of just more slip
A seam is only as strong as the amount of clay actually bridging the two pieces. If your walls are thin, that bridge is thin too, no matter how well you scored it. A small coil of soft clay laid right along the inside seam gives you extra material to blend into both sides. You're widening the bridge, not just gluing the edges.
I use this on the inside of boxes where the wall meets the base, on the inside of cylinders, and honestly on most joins I'm not fully confident in. Which, if I'm honest with you, is most joins on a piece taller than a mug.
How to do it
Roll a coil that's thinner than you think you need. About the diameter of a pencil, maybe a little less. People want to reach for something fat and reassuring, but a fat coil is hard to blend in cleanly and it'll show as a ridge under your glaze later. Thin, then add a second one if you need it.
Score the seam and the coil both. Yes, still. The coil is clay meeting clay just like everything else, and it doesn't get a pass because it's small.
Lay the coil into the inside corner of the join and press it in with your thumb, working in one direction. Don't mash it flat all at once. Go slow, overlapping your thumb strokes like you're smoothing frosting. You're not trying to make the coil disappear instantly, you're working it into both surfaces until there's no visible seam between coil and wall.
Blend outward from the coil in both directions, feathering the edges so there's no ridge where the coil stops being coil and starts being wall. A rib tool helps here if you have one, but your finger works fine too. This is exactly the kind of job a butter knife handles just as well as a $40 rib — I don't think you need the fancy tool to start.
Check the outside of the join too. If you can see a bulge or a line pushing through from the inside work, smooth it from the outside before it sets up. You've got a short window here before the clay stops cooperating, so don't wander off.
One thing I want to be honest about: this will not look perfectly invisible from the inside. You'll see a slightly different texture where the coil went in even after you've blended it. That's fine. Nobody's grading the inside of your pot for symmetry, and — this is one of my actual opinions, not just a comforting thing I'm saying — I don't think you should be chasing invisible seams and machine-smooth walls anyway. A little visible evidence of the build is part of what makes handbuilt pottery look handbuilt. Save your perfectionism for making sure the thing doesn't crack. Let the seams look like seams.
Where people get in trouble
The most common mistake is adding a coil that's wetter than the walls it's joining. If your walls have firmed up while you were working on something else, and then you press in a coil straight off a damp ball of clay, you've got the same mismatched-moisture problem from a couple lessons ago, just in miniature. Check the coil against your wall with your knuckle before you commit it. It should feel close to the same.
The second most common mistake is rushing the blend because you're excited to move on. I get it. But a coil that's laid in and half-smoothed is worse than no coil at all, because now you've got a weak seam with a bump on it.
This is a good place to bring up something that changed how I think about supervising a room full of clay and good intentions. I ran a youth activity years ago, pinch pots, fourteen kids, and I'd budgeted four pounds of clay per kid like a reasonable person. It was gone in twenty minutes. Half of it ended up ground into the gym floor because nobody was watching moisture or waste, they were just having a great time smashing clay around. What I took from that, and what applies directly here, is that speed and enthusiasm are the enemy of a good join. The kids who slowed down and worked one seam at a time ended up with pots. The kids who were racing ended up with clay on the ceiling. Coil reinforcement rewards the slow people. Be a slow person for this part.
Before next time
Pick one piece you've already joined and add a reinforcing coil to at least one seam, just to feel the difference between blending a coil and blending a plain slip join. It's a different motion, and you'll want that in your hands before we build something that actually depends on it.
~erin