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Frequently Asked Questions

Glazing FAQ for Abbots Midfire Glazes

How much water should I add to the powder?

Add 1Kg of glaze to 1 – 1.25 litres of water. This will vary from glaze to glaze. Remember that it is easy to add more water and not so easy to take excess water out. It is therefore a good idea to withhold some of the mixing water for fine adjustments of the glaze density after the initial mixing has occurred. The glazes should have the consistency of thick cream when mixed and sieved (80#).

A paint stirrer on a power drill or battery drill is hard to live without.

How can I prevent the glaze settling on the bottom?

The glaze composition is largely determined by the effects that characterise that glaze. Consequently some glazes suspend easily in the bucket and others need help. The first rule is to avoid over-watering the glazes as there is no way that a very thin glaze will suspend well. Some glazes with very low clay content can be treated with bentonite and a flocculant to aid suspension. Our preferred flocculant is plaster of paris – it is cheap, most of us have some in the studio and the effect is long-lasting. Alternatives are Epsom salts and calcium chloride. Pre-disperse the flocculant in water and add the resulting slurry gradually to the mixing glaze. As a rule of thumb you might use one or two teaspoons of plaster per bucket of glaze. Adding bentonite (in similar quantities) can also contribute improved suspension and better bound glaze surfaces. Add the dry bentonite to water, blitz with a milkshake maker (or mix by hand and stand overnight) and also add gradually to the glaze until the right smooth creamy texture is observed. This sounds complicated but it becomes second nature after a while.

 If your glaze has settled into a hard layer with clear water on top, first scoop off (and reserve) most of the clear water. The glaze can then be (manually) redispersed in the remaining water to the desirable consistency. Add back as much of the reserved water as needed. Glazes that have settled like this will almost certainly need the bentonite/ plaster treatment to keep them suspended. They should have the consistency of yoghurt when they have been allowed to stand for a few days but should be easy to redisperse with hand mixing.

How do I set up a brushable glaze using Universal medium?

This medium is the basis of all Abbots brush-on glazes.

Any dry glaze material can be dispersed in this medium (rather than in water) to produce a thixotropic gel suited to brush application. This enables multiple coats of glaze of one or more varieties to be applied without risk of peeling or blistering. The risk of crawling is lessened due the strong bond between glaze and body.

We suggest adding glaze to medium in a ratio of 1-1.3 parts glaze to 1 part medium (by weight). Vary these proportions or add a little water to achieve the density and brush-feel that works for you.

Disperse the glaze in the medium using a stick blender or power mixer. Sieve through an 80# sieve once or twice before using.

 

How thick should the glaze application be?

Glazes are the clothes we dress the pot in. Do what looks good. Some glazes (like fake ash) need the thinnest of applications and others need a good coat to look their best. Test carefully. Think about gravity and your kiln shelves. Use dry (matte) glazes on vertical surfaces or thinner applications of others. Avoid layering on vertical surfaces and the backs of bowls and plates until you are certain you can predict the outcome. Test lots.

How should I apply the glaze?

Without fear! Dip (quickly) pour glaze from a jug or cup overlapping deliberately or randomly. Trail from a slip trailer (squeeze bottle) or brush it on. Spray if you have to. Glaze and fire as often as you can – only with practice will you develop the confidence that brings success.

Will the glaze run?

Often – yes. The various glazes in the range all have different fluidity – the Abbots Handbook is a guide. Exploit the fluidity on the insides of bowls and plates and on flat surfaces. The fluid glazes interact with one another and move down the sides of bowls etc to create dynamic and unexpected effects. Take care on the outsides and on upright shapes. You will learn to anticipate and manage the behaviour of even the most fluid glazes. Stand your pots on sacrificial tiles or plates if you expect trouble.

What about layering?

Layering is where the magic starts. We have explored just a few of the possible permutations possible and some really exciting results are possible. We are particularly excited by the notion that individual potters will develop their own unique combinations which will become their recognisable trademark. Use every opportunity to discover what happens with 2 and 3 layers of glaze. Remember that when you are building layered surfaces they are often enhanced by splotchy and uneven application.

What temperature should I fire to and how long should I soak?

We fire as follows:

Ambient to 200C                                        100C per hour

200C to 1050C                                            300C per hour

1050C to 1200C                                         80C per hour

soak at 1200C                                             30 minutes

1200C to 1050C                                         80C per hour 

(fire down)

1050 – 900                                                 fast as possible

900C                                                         Soak for 1 hour (Iron glazes)

Cool

 

What clay bodies will give the best glaze results?

For bright fresh glazes use Primo PW20, Primo Porcelain or Decopot Bisque. Expect quite different results on stoneware clay – we have seen some lovely effects with the high iron glazes on raku bodies.

Can I fire in a gas kiln?

Yes. A few glazes may not like heavy reduction but lots of potters use gas kilns successfully.

Can I fire in reduction?

Probably not – but it could be exciting to try some test pieces in reduction firings. Treat these as experimental.

Can I mix the glazes?

Yes – but be prepared for a surprise. Test tiny quantities on non-critical pieces first.

Where can I buy Abbots Midfire Glazes?

Botany Pottery Supplies in Auckland, Cobcraft Supplies (mail order) Decopot Limited, Wellington Potters Supplies.

Why brushable Glaze?

Brushing offers a whole range of opportunity. Apply glaze to awkward sculptural pieces, build layers, get kids involved, get a lot done with a small glaze volume.

Are the glazes toxic?

Some glazes contain high levels of barium carbonate which is toxic. The website and Abbots handbook identify these clearly.

Glaze workshops.

Contact Paul at Decopot to arrange a demonstration to your pottery club or group. A small fee is charged for distant locations and is intended to recover travelling and accommodation costs. If workshops can be arranged in neighbouring locations and only a day or two apart costs are not significant.

 

CLAYBRIGHT UNDERGLAZE

  1. Q: Claybright Underglazes are supplied in two versions. Which one is right for me?

A: Generally potters who intend covering the underglaze with a clear glaze (Abbots Clear Glaze) and who decorate on bisque will use RED CAP colour. This will not seal the bisque surface when applied and can be dipped into the clear glaze when dry (allow a few hours or stand overnight). If the colours are fired without a covercoat on non-functional pieces they will behave as coloured glazes at cone 3 - cone 6. Potters who paint onto greenware or who require the extra colour density of the WHITE CAP paints will prefer these. These are generally subjected to a hardening firing (850C - 1000C) before glazing. This hardening process binds the colour to the pot surface and leaves it strongly attached but completely porous. These colours will give a range of velvet and satin effects if left unglazed and fired to cone 3 - cone 6.

PRIMO CLAYS

  1. Q: I am a thrower and like to use colour to decorate my work. Which clay is right for me?

A: You could use Production White version PW-10. This is a lovely white-firing clay and a dream to throw. It is great to throw, dries quite quickly and handles and knobs stick well. At 1150C to 1180C it is a good fit with ABBOTS CLEAR glaze which will show any underglaze colours well. At this temperature it will have a water absorption of about 3% and be quite durable for tableware. At 1200C PW-10 will be vitreous. care should be taken to match it well to glazes at higher temperatures as those with very low melting points such as ABBOTS CLEAR will seal the body and bloating could occur. With feldspathic glazes this body will handle temperatures up to 1300C and be translucent where thin.

   2.  Q:  I like ultra-white translucent porcelain. Which body is best for me?

A: We have 2 alternatives. MID-FIRE PORCELAIN will be vitreous and translucent at 1200C. It is a great match with ABBOTS CLEAR  and is a delight to throw. HIGH-FIRE PORCELAIN will be translucent just above 1200C and will perform well in firings up to 1300C. Victor Greenaway described this as the nicest porcelain he had thrown with.

   Q: I throw big pieces and fire high. Which clay is right for me?

A: Talk to us about our WHITE STONEWARE and BUFF STONEWARE clay bodies. These are respectively very white and biscuit coloured. Peter Smith at Whangapots in Whangamata is a fan of the white stoneware for his large-scale work.


Using Glaze Stains


Using glaze stains.

These may be used to colour various glazes with additions from 0.2 to 10%. Remember that each stain has its own set of preferences when it comes to the glaze chemical environment. Some will perform well in almost any glaze formulation, some may prefer high calcium environments and some are intolerant of boron or zinc. Abbots Clear is a useful glaze for colouring with pigments – especially blues, turquoises and greens. Even reds and yellows may work well at lower temperatures. This is personal research territory but sites like Digitalfire.com offer excellent information.

For newcomers to decorating with underglazes it is safest to start with proprietary products like Claybright whilst developing capability to make their own. Most underglaze manufacturers have significant investment in their technology and closely guard that IP.  Some of the characteristics that are important in underglaze products produced for sale may be less important to individual users and these need not be a barrier to producing your own materials. Decorators can be successful by dispersing stains in a carrier comprising clays and frits.

Be prepared for a long, possibly never-ending regime of testing if you wish to master ceramic glaze technology. The answers you want are seldom readily available but must be discovered.