Greenware drying in Calgary's dry prairie air: schedules, damp boxes and a firing log

What to take away

Ask how the shared kiln schedule works

Calgary potters who do not own a kiln usually get access in one of three ways: a City of Calgary arts centre course, a university continuing-education course, or a private studio that rents shelf space and kiln shares. The two city arts centres, North Mount Pleasant Arts Centre and Wildflower Arts Centre, run ceramics studios for registered students, and the North Mount Pleasant studio is currently full. Alberta University of the Arts teaches ceramics in Calgary.

Costs come in two parts. A city arts centre usually bundles studio time and firing into a course or season fee. A private studio usually charges a shelf fee plus a per-load firing charge. Ask for the current rate card, and ask how many loads run each month, because that number sets your drying deadline.

Ask three questions before you join. Who loads the kiln? Who decides the schedule? What happens if a piece is still damp at loading? The answers show how much control you have over drying time.

A shared kiln also sets the firing temperature. Community programmes often run one standard cone for everyone, so your drying and your clay body have to suit that target. If your greenware is not bone dry on the loading date, it waits for the next load, which can be a week or two away.

Why dry prairie air speeds greenware drying

Calgary sits in dry prairie air for much of the year, and that air moves moisture out of clay quickly. A mug that takes several days to stiffen in a humid studio can firm up much faster here.

Indoor humidity is often low in winter, when heating dries the air further. Greenware left on an open shelf loses surface water fast, and the rim stiffens before the base. A cheap hygrometer on the studio wall shows the actual humidity, which tells you more about your drying day than the outdoor forecast does.

That fast skin is useful for some work. Handles attach cleanly when the pot is leather hard, and a firm rim takes a stamp or a spout without slumping.

The same speed works against you. When the outside of a wall dries before the inside, shrinkage differs through the thickness, and the pot can pull itself apart. A chinook can change indoor humidity within hours, so check the forecast from Environment and Climate Change Canada before you plan a drying day.

Cracking and warping risks from fast drying

Fast drying causes most of the faults that Calgary potters see before a pot reaches the kiln. The common ones are predictable.

S-cracks appear in flat bases when the base dries faster than the walls and shrinks away from the centre. They often show up after bisque, when the damage is already done.

Warped rims and oval plates come from uneven shrinkage across a wide, thin form. A plate dried in moving air can lift at one edge while the centre stays flat.

Handles crack at the join when the handle dries faster than the wall it sits on. Attached parts, spouts and lugs can pop off for the same reason, and coils joined at different moisture levels separate as they dry.

Some of these faults look like kiln faults. Check the drying stage before you blame the firing.

Slow the drying so the wall dries evenly

The goal is to slow surface drying so the whole wall loses water at roughly the same rate.

The table below gives rough planning ranges from studio practice, not measured data. Airflow, indoor humidity and a spot near a heat register can each move a pot by a day or more.

A damp box buys you time. You can throw on Monday and trim on Thursday if the pot stays in the box, which matters when your shared kiln slot is fixed.

Build one from a lidded plastic storage tub, about 60 by 40 by 30 cm. Put a plaster slab or two damp sponges in the bottom to hold humidity, and keep the lid closed. Pots stay leather hard for days.

Clay body matters too. A grogged stoneware body usually dries more evenly than a smooth porcelain, and glaze choice does not fix a cracked base. Check the body's grog content and choose one that suits thick bases and wide plates.

Time kiln loads around Calgary weather

A warm chinook can drop indoor humidity and dry greenware in hours. A cold snap keeps windows shut and slows drying. Your schedule has to absorb both.

Book kiln time with a buffer, not on the last possible day. If the arts centre or studio loads on a set day, aim to have greenware bone dry two days before, then keep it wrapped until loading.

Watch the forecast for the week before your slot. Environment and Climate Change Canada publishes the local forecasts and weather data you need.

If you fire at home between shared loads, treat those sessions as a test of the kiln and the drying routine, not a race to finish pots. Test tiles and small forms dry faster and fail cheaper. Home kiln installation is governed by Alberta's electrical rules, so confirm them with the authority before you wire a kiln.

What to log so the next batch dries evenly

A firing log is the habit that separates potters who repeat results from potters who guess. In a shared kiln you cannot control the firing, but you can control and record the drying.

Log the greenware weight when it comes off the wheel and again before loading. Weight is a better dryness test than touch, and it costs nothing.

Record the drying days, where the pot dried, and the weather that week. Note whether it was wrapped, in a damp box, or open on a shelf.

Record the firing result: bisque cone, position in the kiln, and any crack, warp or blister. Then compare batches.

After three or four loads you will see your own pattern. Perhaps open-shelf drying cracks plates but not mugs, or damp-box drying adds two days but removes S-cracks. A shared kiln gives you less control, so your log becomes the most reliable record you own.

Common questions