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Gilhouse Pottery Blog Post


What is a damp box and why do I need one?

I decided to write this post for my potter friends, old, new, and those yet to be met, for whom I've described the importance of damp boxes in my pottery studio.

Potters know that timing is everything. Our clay needs to reach particular degrees of dryness before we can move from freshly made to trimming and adding handles, embellishments, carving, etc. Too wet and the piece distorts from being touched, too dry and we risk insecure handle attachments and cracked connection points or joins. Our environments play a part in this Goldilocks story. Here in my Wisconsin basement studio, dry times are affected by the season because of changes in humidity. Potters in Arizona face different conditions. Time is an issue as well. Potters can spend a day making but won't have time to work on the next steps for days or weeks. Yes, we can cover work in progress with plastic or buckets, but what if we want the work to dry to a certain state and then wait for us for a while? Enter damp boxes.

Damp boxes are easy to make. First you need a water proof sealed container that is preferably air tight, and then you need plaster. You can use pottery plaster, but I've been using Plaster of Paris that you can find at any home improvement store like Home Depot, Lowes or Menards. I've seen potters who make the plaster slab in a form so that they can remove it from the container, but I just mix up the plaster and pour it right into my airtight plastic container. I'd suggest the plaster be at least an inch thick, I go closer to two. Just mix up the plaster, pour it in and give it a good amount of time to cure. It doesn't even have to be perfectly flat. Once the plaster is dry in a few days, you have a damp box!

Next you should pour a little bit of water onto the plaster to create your humid environment. When you do this, you'll probably hear a really cool sound as the water is absorbed by the plaster, I really like the sound. Glug glug. There shouldn't be any water standing on the top of the plaster because this will "eat" your pieces. I know this from experience, more on that in a minute.

Put your pieces into the damp box and seal it. As they sit in there waiting, they will "even out" in moisture level, but most importantly they will be held in a leatherhard state, more or less, depending on how humid the damp box is inside. One story I've told over and over is how I stored a piece in a damp box for more than six months, without opening it, and when I finally decided to work on it again, it was a perfect leatherhard. This is why you need a damp box.

There are three damp boxes in my studio because I do sgraffito. My first is an old chest cooler. At this point I use the cooler to store extra handles that I've made as well as pieces that I don't have time to trim, or otherwise deal with right now, or I'm thinking about putting into the reclaim bucket. The cooler isn't as airtight as my other boxes, so I have to check the work and mist down the inside of the box (top and sides) to get them back where I need them if they get too dry. More on that below.

My favorite damp boxes are Sterilite containers that we found at Menards but are widely available. They have a seal on the lid with clamps that create that desired airtight environment.

In my sgraffito process I throw 12 mugs, trim and handle them, then they sit in the damp boxes where they "level out". For what it's worth, I don't need to level out my other work, but if I were in a dry environment, I may need to. Really they're just waiting for me, but they do level out moisture wise. When I'm able, I put on the underglaze, let them air dry further, and return them to the damp boxes to hold for later. In my photos you may notice that I've labelled my damp boxes "Stasis Chamber One" and two. That's because I'm a little geeky, but the mugs are truly in stasis until I'm ready for them. When I want to start scratching some mugs I usually need them to air dry for a while, which I do, but I have another Sterilite box without plaster in it that becomes my "ready to go" box, still on hold but only for days. I've been trying to find my "perfect" level, humidity-wise for sgraffito, so I put a cheap humidity meter in that box with the mugs. It's less than 95% humidity that works for me. The no plaster Sterilite box will hold them for a few days, but not months. I can carve about three mugs a day and so this works great for me.

Another cool thing you can do with damp boxes is "undo" a timing mistake. If you put a too dry piece into a damp box with plenty of moisture, over a LOT of time it will return to leatherhard! Here's more about that lesson I learned. So we've all done it, we made a cool piece and we let it get too dry before it reached its intended potential. I was looking to fix my mistake fast (there's no rushing in pottery) and my piece was too dry so I poured a ton of water into my cooler damp box, made a little lake, and I put the bone dry piece in. :) Moisture good, lots of moisture must be better, right? No. My pot disintegrated. Lesson learned.

Yes, you can restore a dry pot to leatherhard, but it needs a good amount of time and it can't be rushed. Make sure your plaster is saturated, get a spray bottle with a mist setting. Mist your pot, mist the sides and top of the damp box and wait. Check the piece and re-mist as needed. It takes a long time but it can be done, and most importantly, done evenly.

I guess I'll mention cleaning and safety, though it's not a big concern to me. Yes, the plaster can get discolored from the clay, underglazes and evidence of bacteria. Sometimes I wipe off the plaster's surface with a damp sponge and it's fine. Yes, if I let underglazed mugs sit in a damp box for months they can develop a dusting of a white substance that I think many assume is a mold. Strangely, there's not white dust on unglazed pieces that have sat for months. I'm not convinced it's mold, it could be a salt or a calcium or something from the plaster (I'm not a scientist), but in my experience, I'm able to brush off the white stuff with a makeup brush and move on. I'm not concerned about my own exposure, and in the kiln, anything organic will die.

So now that you know what a damp box is for, think about how adding one to your pottery practice could improve your process. Can you make a bunch of handles and store them to use later on? Yes. Can you press a bunch of sprigs and keep them for later? Yep! Can you make a piece that you're not sure of and postpone a decision? Yeppers! Can you really be a potter if you only have one day a month to work on it? YES!!!

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