Glazing Guidelines & Tips2018-10-25T08:57:53+00:00

GLAZING

CLEAN dry bisque (no dirty, greasy fingers), wipe bisque with damp (not wet) sponge.
NO glaze within ½ inch of the bottom. Either wax the bottom or clean it after.
Stir the glaze (30X at least for the first time, stir again right before each use)
Dip, pour, or paint on glaze to ‘postcard’ thickness.
Clean up buckets, brushes and workspace.
Measure your piece and add the right number of glaze stamps. All pieces should be signed!
Put it on the shelf to fire.
No glaze down the sink…wash in glaze wash bucket.
PLEASE USE A NOTEBOOK and write down exactly what you did to decorate and glaze the piece. What glaze(s), what order, how many seconds did you dip the piece for, did you dampen it first, what did the glaze coat look like, how far up or down on the piece did each glaze go…. just make a rough sketch and label the glazing steps. Glazes look very different if they are thin or thick or if they are over or under other glazes. You think you will remember, but you won’t remember exactly … and one day you will have an amazing piece and everyone will want to know how you glazed it…..be prepared to share that information!!!!
ADD NOTES TO THE STUDIO BINDER. If you had a great glaze combination or great glaze result please share it. Likewise if you have a problem like crawling or crazing or running or if you think a glaze is too thick, too thin, too lumpy, leave a comment so it can be investigated and maybe fixed.
Three major glazing problems:
glaze too thin  ugly
glaze runs off the bottom of the pot
glaze crawling

“Goldilocks Glazing”
Glaze thickness:
Glaze coat too thin → ugly. Too thin and glaze can be rough and dry, ugly, and sometimes a different color. If your piece looks bad after firing, you can sometimes add more glaze and fire again.
Glaze coat too thick → crawling, crazing, running, bubbles: Too thick is very bad: Too thick and glaze can crawl and even crack off the piece (sometimes in the kiln) leaving bare spots and messing up the kiln shelves. Too thick can also run off the bottom of the piece sticking it to the kiln shelf….ugggg. Too thick on the inside can cause the glaze to have bubbles where it pools. Very thick glaze coats tend to develop cracks (crazing) after firing (oribe is especially prone to crazing)
Glaze coat just right → beautiful. Just right is about ‘postcard’ thickness. Rough guidelines: one dip ‘instant’ to 8 seconds, or two dips (‘instant’ to 2 sec. each), or a single pour, or 2-3 coats with a brush with each coat brushed in a different direction and waiting for the first coat to firm up/dry before second coat. Use a pin tool or knife to scratch through the glaze to find out how thick it is.

Pot “wetness”:
Pot too wet → too thin glaze coat, poor glaze sticking, slow drying: Too wet can happen when you have already put on one glaze coat, or when the piece is extremely thin, or if you washed the bisque fired piece
Pot too dry → too thick glaze coat, poor coverage in texture, glazing may disrupt sticking of an earlier glaze coat, crawling from dust or grease is made worse
Pot very slightly damp → just right. Use a damp sponge to clean off bisqueware before glazing. For two different glaze coats, let the first coat get mostly dry (dry to the touch, but not ‘bone dry’) then add the next coat.

What is “crawling”? Crawling is when the glaze pulls away from the pot (and sometimes falls off).
Glaze shrinks when it dries (just like dried mud). If the glaze shrinks a lot and the pot of course doesn’t shrink, then the glaze will crack as it dries. The cracked glaze may fall off. Even if the surface isn’t cracked, when the glaze melts in the kiln, surface tension can cause the glaze to ‘bead up’ pulling away from the pot. The cracking and surface tension forces are opposed by tight contact between the glaze and the pot. Very small glaze particles “sucked” onto the pot as it absorbs water help to make good tight sticking between glaze and pot (ironically, these same small particles tend to make the glaze shrink more).

Conditions that promote crawling:
Glaze is very thick !!!!
Glaze applied on top of another glaze. This can be problematic for several reasons:
two coats of glaze are likely to be thick…. maybe too thick
the first glaze may make the piece too wet
if you let the first glaze dry to bone dry, then the water from the second glaze can loosen the adhesion of the first glaze. Some glazes shrink a lot but also stick really well (so no crawling) while others shrink less and stick less (still no crawling) but put the shrinking glaze over the poorly sticking glaze and there will be trouble!
Glaze applied to a piece that is wet. When glaze is applied to a drier piece, the movement of water into the dried bisque ‘sucks’ the glaze right onto the pot surface. If the piece is wet, there isn’t much “sucking” and the glaze just sits on the surface. Since it is not adheared as tightly it is more likely to crack or bead up.
Glaze applied to dirty bisque ware. If there are greasy fingerprints (think hand cream!) or wax (ohh noooo) or dust then the glaze won’t be adhered as well.
Glaze applied to bone dry bisque. Some places (especially if dusty or deep texture) may not wet efficiently on really really dry bisque. So the “sucking” isn’t as strong everywhere and sticking isn’t as good. Wiping with the damp sponge helps both dirty bisque and dry problems.
Melted glaze is very “stiff” with high surface tension. “Bright white” for example (see the test tiles). This stiff glaze property can make any of the above problems worse.
If the problem is just due to cracking as the drying glaze shrinks, you can push the glaze back onto the pot with your finger and rub glaze into the cracks. In extreme cases you can add a little water to suck the glaze back onto the pot. On the inside of a bowl or cylinder the glaze can pull away from the pot without any cracks showing. Push on the glaze on the inside curve with your finger. You will feel if it is loose (your pressure will crack the glaze as you push it back against the pot). WARNING, if it cracks, the glaze is likely to be too thick!!!! If the glaze is too thick or the cracking is severe, please wash all the glaze off your pot, let it dry at least overnight, and try to glaze again another day. The kiln gods and glaze shelves will be grateful! And you won’t ruin your pot.
Take home message: Crawling depends on thickness and which glazes are used. We need to learn which glazes play nicely together. And which are problems:
Bright white: stiff glaze, likely to crawl
Glossy Black: may be a “low crack, low adhesion” type likely to crawl if used under other glazes
V. Edwards semi-transparent: has a lot of zinc which makes crawling more likely.

Why do glazes run?
Glaze is too thick!
Glaze is very fluid when it is melted (some glazes are stiffer than others)
Glaze combination is very fluid when it is melted or it melts at a lower temperature.
Some glaze overlaps are very runny….best to have glaze combinations at the top of the piece.
Any glaze that is very thick will be runny. Glaze combinations are more likely to run than the same thickness of a single glaze (eutectics).

How to treat your feet (so your pot won’t stick to the kiln shelf):
apply wax. Use the wax brushes (not the glaze brushes). Never let wax dry on the brushes. Try a banding wheel or potter’s wheel to turn your pot to apply an even foot-ring of wax. Aim for ½ inch foot (or more!). Let the wax dry. Do not get wax on your pot. After glazing, use a damp sponge to clean all glaze spots off the waxed foot.
clean off glaze (no wax). After glazing press your pot against a large flat wet sponge and spin the pot to rub off the glaze. You can get a very even foot ring this way, but you may need to rinse the sponge and repeat the cleaning several times. Get ALL the glaze off at least ½ inch up the pot. If in doubt that maybe the glaze will run off your piece, PLEASE place your piece on a bisque fired slab that has kiln wash on it. Save our kiln shelves!

Glazes that run — especially in combinations:
Honey and Sin-Sin are very very runny … they are great near rims to make nice streaky drippy runs…. but they will also flow right off the pot.
V. Edwards Semi-transparent is runny (according to test tiles).
Spearmint and Paul’s White may be runny especially in combination.

Some good glazes and glaze combinations:

Turquoise and Slate Blue (either one on top) … rich varigated blue-aqua over white or brown clay.

Turquoise or Autumn over Oil Spot. Gives a nice black variegated (spotted) effect that adds interest to pieces that have clean (not ornate) forms.

Bone (warm) or Paul’s White (cool) over Autumn will break nicely to highlight deep texture marks (but may obscure fine detail or more subtle marks).

Autumn over Toby’s gives a rich warm reddish brown.

Oribe will show up finer textures especially on white clay: note: Oribe will craze…. especially if thick.

Clear over underglaze decoration on white clay (clear is best when it isn’t too thick).

Honey or Sin-sin over any of these will give nice flowing runs.

Please add descriptions of your favorite combinations to the Glaze notes binder (next to the test tiles).

A few ideas:
Consider leaving some bare clay to contrast with the glaze….
You can use wax resist to make designs in addition to just using it to make clean feet.
You can also use wax resist over the first glaze coat to resist a second contrasting glaze.
Or you can use tape to block the first glaze coat, remove the tape and apply a contrasting glaze.

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