Why Thickness Matters More Than Technique

Most glaze faults that land on the shelf at the end of a firing — crawling, pinholing, shivering, a colour that has gone muddy or washed out — trace back to one thing: how much glaze is actually sitting on the pot. Too thin and you get a dry, patchy, underfired look with the clay body grinning through. Too thick and the glaze can crack off the rim, run onto the kiln shelf, or bubble into a cratered surface you cannot rescue.

The good news is that the target is not mysterious. Most studio glazes want a dry, unfired coating of roughly 0.6mm to 1mm — about the thickness of a decent coat of emulsion paint, or a business card. Learning to read that thickness by eye, rather than trusting a stopwatch, is what separates a calm glazing session from a gamble. Dipping, pouring and brushing all get you there, but each leaves its own fingerprint on the surface.

Test Tiles Are Your Real Teacher

Before you commit a finished piece to the bucket, make test tiles. They are cheap, quick and endlessly reusable as a reference library.

• Roll a slab about 5mm thick and cut tiles roughly 5cm x 8cm.
• Texture one half with a rib or a bit of coarse sand — glaze sits differently on texture than on a polished surface.
• Bisque fire them alongside your normal work, so the porosity matches what you actually glaze.
• Label the back with a pencil before firing: glaze name, method, number of coats or dip time.

Now apply the glaze in a controlled way. Dip one tile for two seconds, one for five, one for ten. Brush a second tile with two, three and four coats, masking off stripes with tape so each band is separate. Pour a third. Fire them together and keep them in a box or on a board near the glaze buckets. Within a few weeks you will have a genuinely useful record of what "right" looks like for your clay and your kiln, and you will stop guessing.

Dipping: Even, Fast and Unforgiving

Dipping gives the most consistent film of glaze, which is why it suits production work and simple forms. The catch is that everything depends on the glaze being properly suspended.

Check the specific gravity. A rough guide for many stoneware glazes is 1.40 to 1.50, measured with a hydrometer, though your test tiles are the final judge. If the glaze settles hard, the bottom of the bucket will be thick and the top watery. Stir thoroughly, then let it rest for a few minutes so bubbles rise. Slightly flocculating a glaze with a pinch of Epsom salts dissolved in warm water can improve the cling and stop it dripping off the pot.

Hold the pot by the base or with tongs, lower it in at a slight angle so air escapes, count your seconds steadily, and lift it out in one smooth motion. Let it drain over the bucket, rotating slightly, then wipe the foot with a damp sponge. Watch for drip marks and a thicker bead where the glaze pools near the base — that is where running and crawling like to start. A second, shorter dip at 90 degrees to the first can even out coverage, but keep it brief or you will double the thickness at the overlaps.

Pouring: Control for Interiors and Large Pots

Pouring is ideal for the inside of a vessel, for tall pieces that will not fit a bucket, and for glazes you want to layer. Ladle glaze into the interior, swirl it right up to the rim, then tip it out in one continuous movement so the excess runs back into the bucket. Keep the pot moving as it empties, otherwise you leave a tide line down one wall.

For exteriors, place the pot on a banding wheel or a turntable and pour glaze down the side while turning slowly. You can also hold the pot upside down over the bucket and pour the base first — a neat trick for feet and rims.

Pouring leaves a slightly rippled, fluid surface with visible flow marks. On a matte glaze this can look lovely and handmade; on a high-gloss, it may show as streaks, so give the piece a gentle rock or a quick even-out brush while the glaze is still wet.

Brushing: Best for Detail, Trickiest for Evenness

Brushing is the most accessible method and the hardest to keep even. The golden rule is to never brush back over glaze that is already drying — you lift the half-set layer and end up with a lumpy, dragged finish.

• Use a soft, wide hake or fan brush and load it properly, not just at the tip.
• Apply in one direction, then let it dry to a matte sheen before the next coat.
• Three thin coats generally beat two thick ones; thin glaze flows out flat and hides brush marks.
• Work quickly and overlap each stroke by about a third.

Check coverage by holding the pot up to a window. Thin areas look dull and translucent; correct areas look opaque and even. Brushing is perfect for accents, rims, and glazing the inside of a pot you have dipped outside.

Reading the Dry Surface

However you apply it, judge the finished dry glaze the same way. It should look like an even, powdery coat with the clay colour just hidden. If you can still read the texture of the clay through it, add another pass. If it looks chalky, cracked or crazed before firing, it is too thick — rinse a little off under a slow tap and let it dry again.

Keep notes on every piece. After a couple of firings you will know exactly how many seconds in the bucket, or how many brush coats, gives you the surface you want — and glazing day becomes a pleasure rather than a lottery.