Application Tips

APPLICATION TIPS

GLAZE OF THE WEEK 16

  • PREPARATION

  • WAXING

  • DIPPING OR POURING

  • TOOLS

  • CAUTIONARY TALES

Where to begin? So many choices. Let’s think about the proper application of one glaze to one bisque fired pot. Form is everything, with or without glaze, but glaze can make or break a pot. The best way to learn is to watch an instructor or an experienced potter glaze a piece. This is how one learns what is enough and not too much, a common and costly error.

PREPARATION

First, prepare the bisqued pot by cleaning it. At HPG so much dust pours down from the freeway, particulate matter which is not just organic soil, but also asphalt, rubber and metal car scrapings. This is the road junk which ends up by the ton in the ocean as more and more green space is paved over. It may not burn off. Under a glaze, it could cause bubbling, spitting , dunting, and cracking by reacting with glaze chemicals. Maybe not always, but why take a chance?

Slightly wetting the pot causes a small amount of water to be absorbed right into the pot. This moist surface film helps the glaze become attached to the surface more securely, and can prevent a glaze from being applied too thickly. Take care; a bisqued pot is fragile. Two ways to damp clean a pot are:

  • ÿ  Rinse the pot quickly with water, notice that the water is sucked right into the glazed pot, leaving the surface fairly dry-looking. Rinse as evenly as possible, and not excessivley, or glaze will be uneven or too thin.

  • ÿ  Sponge the pot evenly with a clean, wet sponge.

    WAXING

    The next step is apply wax to the bottom so that glaze can not collect there, causing the pot to stick to the shelf during the firing. Liquid wax is “painted” onto the foot about one half an inch [1/2 in] above the bottom allowing space for some melted glaze to collect if it is a runny glaze. Use wax wherever you want no glaze. The wax is usually purchased as “Mobil-Cer”, a rather thick waxy solution which is diluted for use into the jars used in the glaze area. The waxing works best when it is thoroughly dry, so this is done the day before glazing if possible. If not, wax first, then get the glaze ready while it drys.

    At least one wax bottle will be labelled “Wax with Alumina”. Alumina is aluminum hydrate which does not melt even at cone 10. This is a white powder which settles to the bottom and must be stirred well before applied. It is used to prevent a lid from sticking to the rim of the pot which is similarly waxed. After firing the alumina becomes a dry powder which can be easily wiped off or sanded off. Apply carefully so that none of this gets onto the glazed area where it will dull the glaze finish.

    Brushes for waxing. Any painting brush about 1⁄2 inch wide is OK, and if the bristles are cut to a flat edge it works well. Take care not to drip wax where it is not intended; it is impossible to remove. A glaze will be “resisted” where there is wax. Perhaps rubbing alcohol will take most of it off, but that is not usually available, nor does it remove wax completely. HPG has a supply of brushes near the waxing area. After use the brushes need to be cleaned of the wax to prevent

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build-up which becomes inflexible and hard on the bristles. Cleaning is done by washing the brush in a detergent solution found near the sink or using a bar of soap, then rinsing.

GLAZING PREPARATION

Mixing:
The bisqued, cleaned, waxed pot is now ready for glazing. Time to get the glaze ready. What? The glazes are not all ready? There they are in the vats and buckets waiting to be used? Sorry, this is not how it goes. The glazes are suspensions of at least five partly soluble chemicals. They are not like homogenized milk. They need to be mixed very thoroughly as some of it settles to a thick paste at the bottom of the vat. This is where a lot of good stuff hangs out, so it needs to be blended into the thinner material at the top. There are numerous spatulas, wooden spoons and whisks to help with the mixing, and it is good to test the mixing by stirring with the hand because sometimes stuff hides at the bottom. Wet glazes are not harmful to the skin.

As a glaze ages in a vat, certain ones can change acidity over time becoming more alkaline. Some of the components can settle to a hard pack at the bottom. This has to be loosened with a metal tool and remixed into the rest of the glaze. The use of non-setling agents like bentonite has been added to most glazes, but in spite of this some settling can occur.

A glaze can settle rather quickly again, so restir it before use if some time has passed while doing other things.

Straining: Glazes are strained before being placed in the vats, but some glazes have a tendencey to go out of solution and form tiny hard particles. These need to be restrained. There are appropriate strainers for dark and light glazes. Pour what is needed through a strainer on a rack into a large basin. Remix, use, and pour the rest back into the main vat. Miller White sometimes requires restraining.

The sides of the vat should be quite clean before starting to mix. The previous user should have done this as a courtesy to the next user. This is precious glaze material which needs to be mixed into the main glaze body. Either scrape it into the rest of the liquid, or using a sponge, wipe it down with some water or the glaze itself. In other words, clean the glaze vat after use.

Thickness: The easiest, quickest way to test the thickness of a glaze is to put your hand and arm into it. If you can still see the hair on your arm through the glaze, it is about right. If not, it is too thick, and adding some water is necessary to replace evaporated water in a long standing glaze. If it is too thin, a second glaze application may be necessary. The glaze should be about 2 mm thick on the pot, but this is hard to judge.

Specific Gravity: This is a term used to describe the thickness of a liquid compared to water, set at 1.0 grams per milliliter. Glazes should be about 1.6 times heavier than water (except for Joe’s Green which should be much thinner, more like 1.3. As the glazes are made up new, and periodically, this is tested using a float instrument designed for this, a hydrometer which has a gauge of numbers marked on the side. There are a couple of marked plastic bottles filled with weights in the glaze area for an adequate testing when floating in the glaze container. For small amounts of glazes another instrument is used.

GLAZING TECHNIQUE

There are different ways to glaze a pot when everything is ready. Demonstrations or illustrations are much better than words, however here are some tips.

ÿ Dipping the pot. Simply dip the pot into the glaze for a few seconds, tip it upside down, and allow the excess to drip out thoroughly, until there are no more drips. Then turn the pot onto its foot ring to dry. If the pot is small enough, it can be grasped by the thumb on the rim and the forefinger on the foot, or use tongs. While still wet, the excess drips can be gently wiped off with the finger, and the bare spots where the pot was held can be filled in with wet

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glaze, using the hand or a brush. If the pot is very large, it can be dipped in sections. Sometimes an overlap can be interesting; otherwise when the glaze dries it can be gently scraped to an even thickness with a wooden tool.

  • ÿ  Pouring: Glaze the inside of the pot first by pouring some glaze into it. Drain off the excess. Using a wire rack placed over the vat, place the pot rim down. Pour glaze so that it falls evenly around the outside of the pot. When dry, turn the pot over onto its foot ring. The rim will be a mess. Wipe it with a lightly dampened sponge, and let dry. Redip the rim in mixed glaze. This is the method one must use if the pot doesn’t fit the glaze bucket.

  • ÿ  Brushing: Glazes can be brushed on using a soft-bristled brush. If brush strokes are a desirable effect, a thin coat is all that is needed. A smooth effect by brushing requires two or three coats applied somewhat thickly.

  • ÿ  Spraying: There are a variety of spraying tools available, from a simple blow and spray device to a powered sprayer. The use of the HPG spraying cabinet is recommended. Individuals supply their own nozzles. Usually spraying is done for a certain effect, one glaze as an accent over the other.

FINISHING

Glaze droplets will remain on the waxed areas of the foot. This glaze is removed with a damp sponge after the glaze has dried on the pot. Glaze should not be visible on the waxed area of the pot, and it should be very thin on the unwaxed bottom inside the foot ring. Even a small droplet of glaze will swell during the firing and cause the pot to stick to the shelf, often damaging the shelf.

It is removable, but will leave some unsightly kiln wash on the pot.

If one of the runny glazes has been used, or if the glaze application near the bottom of the pot is rather thick, this glaze needs to be thinned out so that it does not flood the bottom with melted glaze. This can be done with a wet sponge, or by gently scraping or “feathering” with a wood tool, metal or plastic rib. The main glaze will melt down enough to cover the thinned out area.

Reminder: Be sure to wipe down the sides of the glaze vat when finished, and wipe up spilled glaze areas on the outside, the floor, and on the tools.

TOOLS

There are so many ways to apply glaze. Here are some rather essential tools to have on hand.

  • ÿ  Brushes: It is useful to own a set of various size brushes of reasonably good quality for

    a smooth application. Glaze (or wax) is hard on brushes, so they must be kept rather clean. Thin 000 brushes are good for drawing or lettering, on up to rather wide, one inch, for brushing slip or glaze.

  • ÿ  Wood tools: All varieties of wood scrapers, the same as for throwing tools, chopsticks and skewers for applying and mixing slips, carved blocks to imprint a design with glaze. A pencil for sketching or marking.

  • ÿ  Sponges: Small, fine pored sponges are useful in glazing for cleaning excess glaze on the pot. Sponges can be carved to imprint a design. A course sponge dipped in glaze and applied leaves a pattern of its own. Q-tips are handy to touch up or clean off a small area.

  • ÿ  Droppers: A medicine dropper or a baby ear flushing bulb is used for trailing an accent glaze in a fine line. A turkey baster can make a very thick trailing or swoosh.

  • ÿ  Turntable: HPG provides a few turntables for use in applying glaze decorations evenly around the pot.

  • ÿ  Miscellaneous: Leaves with heavy veining, fancy buttons or stamps you can carve yourself for imprinting, broom bristles, cloth, newspaper for easier cleanup, crumpled paper for imprinting, tape or wax for resist designs.

  • ÿ  Books: The good source for ideas, techniques, new glazes. Many can be borrowed from HPG library (ask a member) and old ceramics magazines kept in plastic bins can be borrowed as well. The HPG Glaze Guide notebook has write-ups and photos about HPG glazes.

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DECORATION

This is sort of up to you. Consider the shape and use of your piece. Please refer to previous chapters about underglazes, slips, overglazes with oxides, secondary glaze accents, glaze combos and wax resist.

Pat Harwood 1/2/07 January, 2009 ed. April 23, 2009 Nov 2010

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