Loupes, rubber gloves, careless washer-uppers, subversive gurus and Janet’s ‘wonder glaze’

compiled by Daniel Skeffington

About Surface Therapy

Glazes for Functional Ware is the topic for the third in the series featuring historical perspectives, Australian contemporary use, basic theory and science, further reading references, and a working recipe for you to try. And there’s a new barrier product which enables unglazed bisqued work to be used as if glazed – a development that adds wider scope for more genres to be used as functional ware. Featured artists include Janet DeBoos (ACT), Michelle Lim and Ng Seok Har of Mud Rock (Singapore), Prue Venables (VIC) and Paul Davis (NSW).

Glazes for functional ware with a focus on wide cone range firing

Even a short time spent researching this topic in the literature or on the web would scare the pants off the inquiring potter considering using or developing a glaze for functional use. If we’re not poisoning our users, flakes of glaze might be ingested, lodge in our bodies and become internal cancerous alien monsters – worse, we might poison ourselves at any point of the many steps in making. And even worse still, the glaze we use might not be ‘fit-for-purpose’ – and we don’t want Fair Trading breathing down our necks, do we?

What is difficult and of primary importance in making functional ware (sometimes referred to as domestic ware or dinnerware, both limiting terms which deny the many other functional uses for ceramics), is to use a glaze that satisfies a whole bunch of criteria including, and other than, health and safety issues. These will be discussed here. Further still, if you’re a beginner or have little firing experience, when facing these maker dilemmas you want to start by using a glaze that is tolerant of a wide firing range and also has application on a diverse range of clay bodies – as an insurance for your work’s successful completion and perhaps to make your world a little less stressful. For functional ware, the successful outcome of the surface treatment you will choose for your vessel is ultimately to have ‘utility’ as its core DNA and to be either facilitated or complemented by that surface treatment.

Functional ware beginnings

There is a toss-up amongst scholars of antiquity as to the purpose of the first man-made clay objects. Were they objects of belief and ritual expression? Think Venus of Dolní Věstonice {1} (29,000 – 25,000 BCE). Or were they vessels to carry water from the stream to wash down Mum’s woolly mammoth stew? Whatever the functional purpose first devised, functional ceramic objects have existed throughout the millennia. And it’s now gone full circle with designer ceramic watches! The ceramic material has an enduring currency. Alongside this development pathway there has been an ever-increasing set of criteria in the making of functional ware – from a volume-holding vessel to a non-leaking vitreous body to a product that doesn’t go KaBOOM! when nuked in a kitchen microwave, or an item needed to colour-match the board’s dining-room curtains. The decision-set needed to develop functional ware is only multiplied by the considerations of what glaze to use or what surface treatment to apply.

Modelled figure of a mature woman from Dolni Vestonice, the oldest ceramic figure in the world; on loan from Moravske Zemske Museum. Brno.

Modelled figure of a mature woman from Dolni Vestonice, the oldest ceramic figure in the world; on loan from Moravske Zemske Museum. Brno.

Above: Venus of Dolní Věstonice, Moravske Zemske Muzeum, Brno, Chez Republic; ©Trustees of the British Museum

Occupational hazards – the big one

Top of the Google search list for ‘glazes for functional ware’ is the evils of certain elements (lead, barium, manganese, copper, chrome, lithium, frits containing lead and stains containing unstable toxins) that should be either avoided or treated with great caution when added to glazes. These chemicals are well documented as being toxic and carcinogenic, however it must be added that makers use them routinely, so caution rather than exclusion is necessary. Use your OH&S procedures and confer with the Material Data Safety Sheets when in doubt. As an example of what can go pear-shaped, Janet DeBoos (Emeritus Fellow, School of Art, College of Arts & Social Sciences, Australian National University) published her research on barium, Living Dangerously: barium glaze research project {2}, calling it nasty stuff, and detailing the lack of stability and its toxicity which leads to chronic breathing diseases and mortality; similar to other compounds or cocktail combinations of them. This article was also published later in Ceramics Technical, 1999.

Oh, and don’t forget skin absorption issues associated with these nasties as well, particularly when mixing chemicals or applying glaze. Gloves must be worn! At this point it is worth repeating the previous ‘Surface Therapy’ text on what is commonly known as ‘glaze hygiene’: Always apply appropriate Health and Safety practices and protection when working with glazes and ceramic equipment, and always use a P2 dust mask, rubber gloves and protective eye-ware. For handling instructions, including toxicities of individual glaze ingredients, go to www.msds.com/ {3}.

It’s not only our exposure to these nasties in the making of our pots that’s of concern, but also the care of our customers. When using an object with a glaze made up of toxic elements, an acidic medium like vinegar or lemon juice (think salad dressing) can cause leaching of the metals into the foodstuffs. High alkaline detergents used in dishwashers can also, over time, degrade the glaze surface. The result is not too hard to imagine.

For food safety and for other listed reasons as mentioned above, it’s worth mentioning a new product called Liquid Quartz. It acts as a barrier agent on all unglazed, fired ceramic surfaces, eliminating the need for glazes and allowing alternatively fired objects (e.g. saggar, bisque, pit-fired, raku or unglazed ware) to be used as functional ware. Read more here: http://madeofaustralia.com/products.

Made OF Australia's dinnerware range, saggar-fired with native Australian flora, sealed with Liquid Quartz, diam.11–27cm

Made OF Australia’s dinnerware range, saggar-fired with native Australian flora, sealed with Liquid Quartz, diam.11–27cm

Going further afield, the glaze choices we make may also have a negative impact on our environment. The fumes from firing and the tailings from glaze buckets disappear from us into the atmosphere and oceans, but their legacies may have lasting and toxic consequences on our world. Consider!

The sober, nay macabre, issues discussed above are just ‘scratching the surface’ (my clever segue into our next section), but before reading ahead you might refer to: Digitalfire Reference Database, (Technical Articles) – ‘Are your glazes food safe or are they leachable?’ {4}

Extended considerations

What are some of the other considerations for your functional ware surfaces? A humourous anecdote of a certain writer highlights an obvious one: Imagine an exhibition of new work – vases and bowls proudly setup on plinths in a beautiful space the night before the opening. The vases were filled with water and flowers to complement the forms, photographs were taken and the doors locked ready for the 10am official opening the next day. Next day there was a swimming pool where the floor should have been. (Bugger those hairline glaze crazings and unglazed foot rims!) DOES YOUR WORK NEED TO BE VITRIFIED? If so, go to McMeekan’s {5} lesson 101, definitive guide to testing and specification of clays and raw materials. Note well – a glaze should never be relied on to ‘seal the deal’, that is to 100% vitrify a pot, but the glassier the better! Take my advice, avoid embarrassment, pre-fill your vases before you take them anywhere near your curator or gallery directory and get yourself a loupe to closely check the glaze minutiae.

But wait there’s more – think about the following:

• Functional ware with crazed glazes (planned or otherwise) might also be porous, a combination that is potentially a breeding ground for nasty bacteria and subsequent human exposure.
• Is the body and glaze strong, robust and substantial enough to be ‘fit for purpose’? The most beautiful micron-thin porcelain vessel might not be appropriate for eating out of, or it might not provide sufficient insulation to prevent skin scalding. Can your ware stand up to the rigours of cutlery scratching the surface, sink stacking by a careless washer-upper, or food and chemical staining leading to degradation of the surface?
• If your functional ware is required to be duplicated, can your design be appropriately moulded or production-thrown and made and glazed economically? Have you made it as easy as possible in the design brief to produce the desired outcome? Is the making and glazing time efficient? Can you use a cheaper clay body?
• Does your design fit the brief? Will the spaghetti marinara spill off that square plate with no rim? Will the wine jus pool in that spot next to the Wagyu beef medallion, just as planned?
• And what about colour and decoration? Does the ware’s appearance suit the menu to be served the flowers to be plonked in, the décor, the user, the ‘now’ aesthetic?

Prue Venables, Black Colander, 2011, h.24cm, w.27cm, d.18cm, Skepsi Gallery exhibition; purchased by Castlemaine Gallery, VIC; photo: Nicholas Hannah

Prue Venables, Black Colander, 2011, h.24cm, w.27cm, d.18cm, Skepsi Gallery exhibition; purchased by Castlemaine Gallery, VIC; photo: Nicholas Hannah

There’s no contemporary artist maker like Prue Venables {6}, the subversive guru of Australian domestic ware, to get you thinking about the criteria for successful functional ware. Her approach questions our use of clay and glazes in their place as functional pieces. Is that pierced bowl or ladle useless, or is it a very functional sieve or a slotted spoon? What is needed to make a functional piece useful? What is useful? What has been the thinking in it’s making? What syntax gets the message heard and understood? Venables has responded to our material world – beauty, ambiguity, form and dysformia. She invites our own response – Venables the funster, the provocateur!

Case study – a functional ware focus of a new enterprise in Singapore

Mud Rock

Michelle Lim and Ng Seok Har with their functional ware, Singapore, January 2016

Michelle Lim and Ng Seok Har are makers who started their clay enterprise, Mud Rock {7}, in Singapore with the specific focus to deliver commissioned functional work for this idiosyncratic and bustling foodies paradise and for the top-end, one-off dinner set buyer. “We have identified the trend for restaurant managers and their chiefs to deliver a richer experience for their diners. It’s a wholistic approach involving market gardeners, butchers, provedores, interior designers and ceramic artists.” They also supply a range of work for the new Singapore National Museum of Modern Art gift shop, important for the cash flow of their start-up business. Typically, their work is client-brief based. “We conduct our commissions as if we were running any business,” says Seok. “It is not only important to deliver the outcome clients expect of us, but we see the client as a springboard to future ‘word of mouth’ business. We need to get the brief right and to do this we have to ask the right questions. And most of these are about expectations.”

Seok’s questions:
• What is the ware to be used for?
• What is the extent of the use?
• How will the ware be maintained/cleaned?
• Are there limitations imposed by the table/furniture?
• What kind of food is to be served?
• What are the other elements of the table service to be complemented – the flatware, linen?
• What are the colour and surface decoration requirements and ideas?
• What variations of the design are required – soup, dinner, entrée plate etc. etc.?
• Who are the decision-makers in the final selection? What are their individual requirements – for example, the chef will have different expectations from the owner?
• To what extent is artistic expression in the work expected?

Michelle, a protégée of DeBoos and a graduate of Canberra’s ANU, discusses the esoteric nature of the brief: “We find that our clients want original, unique designs, striking and noticeable, often to a point where the ware adds to the brand of the restaurant, yet the pieces must complement the food first of all and then the whole ambiance, but always being careful not to overpower the food presentation. The work also needs to satisfy certain performance design criteria. Our work must inhabit the spaces they are used in. The fun part starts when we develop our test samples based on the brief. We take a lot of time to deliver on what we believe are the client’s expectations so our model- and maquette-making and glaze testing is a significant part of the delivery timeline. Getting it right means we have listened to the client. Making and selling functional ware is a new ballgame for us. We are bespoke makers now, where previously we made according to our own aesthetic and offered it for sale – obviously to someone who connects with it. This is a new dynamic for us. Our response is very much manifest in the glaze and surface decoration we use and is one of the most important features of our ware.

Decisions, decisions, decisions
Go to the Decision Algorithm to help sort through the criteria of glaze selection for functional ware.
Download the PDF HERE.
glazing algorithm

Master class – Australian setting

Like Singapore’s Mud Rock, many contemporary Australian makers have taken the challenge of producing functional wares for dining settings and for very similar reasons – brand identity, points of differentiation, immersive dining experiences etc. All no doubt grapple with the complex considerations we have so far highlighted, yet each brief would have its own idiosyncratic requirements to overcome. Nonetheless, success can be sweet: check out the family enterprise of Robert Gordon (www.robertgordonaustralia.com) to view their extensive range of functional ware. Also Paul Davis and Jacqueline Clayton, who are based in Newcastle. They deliver commissioned work for high-end establishments such as Sydney Opera House’s Bennelong restaurant and the Quay restaurant through their design company ‘Press to Play’. See HERE for images of their work. {8}

These success stories might seem all too high-end for the casual or mid-skilled artist-maker, but consider them demonstrative of outcomes that have addressed the before-mentioned criteria. So in making a dinner set, vase, bowl, light shade, whatever, for yourself, your mum or your market-stall buyer, the same decision-set can be a guide.

Glaze theory and DeBoos’ ‘Wonder Glaze’

“To achieve an acceptable wide cone range of firing glaze, potters automatically reduce the clay content; however the alumina in the clay as part of the glaze formulation actually keeps the glaze stable the higher it is fired. So make sure your clay content is available in useful proportions. Although reducing the clay content might drop the glaze melting temperature to earthenware, when it is fired higher it will melt and run more quickly as the melt will be less viscous. For this reason as well, having fluxes that act over a range of temperatures is desirable; it means that they ‘even out’ the melting range. For example, boric oxide in the frits and zinc are very good over mid-range, as is calcium from about 1100°C (cone 03) upwards.”

Like the chemistry interplay of materials above, other factors affect a glaze’s firing temperature; or put another way, where it appears at its best or how you want it to finally present, this is it’s ‘aesthetic maturation’. Knowledge that a ‘mature’ glaze can be part of a spectrum from softening to melting to running; that a target temperature is a function of both heat source and time where time affects the rate at which crystals in the material will disassociate and become flowing, therefore the quicker or slower of both the firing and the cooling will affect the glaze outcome; and the testing results you have secured from your trials – all of the above will bring about knowledge of the firing range of your glaze.

For an excellent short account of the science of glaze temperature determination go to Digitalfire Reference Database. Technical Articles: What determines a glaze’s firing temperature? {9}

Janet has used her Wonder Glaze {10} – so-called for its forgiving properties, versatility and happy outcomes – for an extended period of her practice. It was also featured in her first volume Glazes for Australian Potters. {11} “It’s a clear glaze with an optional tin oxide additive for white (Note: with tin, in a reduction firing it will lose some of its opacity as the tin becomes a flux), however overall it’s a great performing ubiquitous glaze. It seems to perform very well on functional ware and has the added benefit of having a wide cone range maturation profile. It’s a gift that keeps on giving.”

Janet has provided three glazes for your consideration. The first is discussed further below and the second and third, both essentially stoneware glazes, are attached to this article as glaze sheets, as is the first. Go HERE to download the PDF Glaze Sheets.

Keeping in mind the above glaze behaviour and rationale, Janet’s basic clear glaze formula follows. It’s poignant to note the suggested firing cone-range of this glaze, i.e. 01–8. This is a stretch of temperature maturation of 120°C – significantly wider than many glazes. The benefit here is flexibility, though obviously the ‘take home’ appearance and your satisfaction with your output will differ within this range. (Your author’s tests produced a consistent result between cone 01 and cone 6 as per the glaze test results shown below.)

DEBOOS CLEAR: Go HERE to download the PDF Glaze Sheets.
Fire cone 01–8 oxidation

• Ferro frit 4108 (formerly 4508) – 50 (flux; low alumina, high calcium borosilicate frit)
• Potash feldspar – 20 (also called Orthoclase; flux, melts at 1200ºC)
• Ball clay – 20 (highly plastic clay; ball clay vitrifies between 1100–1200ºC)
• Magnesium carbonate (light) – 10 (Opacifier up to 1170ºC then acts as frit. ‘MgCO3 light mixes better in the glaze slop’ {12})

Janet’s wise saws and variations

• A ‘nice to have’ addition is tin oxide – 10 parts. This will have a whitening effect as tin is an opacifier and whitener.
• With the tin addition and used on a terracotta body at mid-range, i.e. Cone 01 – 5/6 (1140–1200ºC), it delivers a smooth opaque white glaze which breaks to tan where applied thinly. If the clay body is white, there is no break. The glaze can fire to cone 8 producing a higher gloss and a slightly pearly whiteness with the same body/colour responses. Note: depending on the clay body and the firing schedule, firing higher than cone 8 (1250ºC) can sometimes lead to blistering.
• The addition of 1 part red iron oxide makes the glaze a cream colour but with a tan break on edges. This break is due to the magnesium carbonate ingredient, which is also responsible for crawling if the glaze is applied too thickly at the lower temperatures.
• Colourants to try: copper (light greens): 1–3 parts; chrome (greens): 0.2–1 part; cobalt (dark blues): 1–3 parts.

With the presence of the magnesium in the mix, the above colourant additions might be compromised in the following ways:
• Copper tends to ‘grey’ rather than ‘green’ at the lower temps (1140–1160ºC) Cone 01
• Chrome tends to ‘browns’ rather than greens
• Cobalt tends to produce mauve rather than sharp blue, (but as the temperature gets higher – the ‘glossier’ and ‘bluer’ is the outcome because the ‘mauveness’ is only present in the crystallisation of the glaze during cooling, i.e. the faster the cooling,the ‘bluer’ the results; the slower the cooling the lighter the colour).
• To avoid the effects of the magnesium on colour response, it can be substituted with zinc oxide (glassier results and some colour compromises), calcite (slightly glassier and colours usually pretty true), dolomite (midway results), barium carbonate (good results with glossier and brighter colour responses) or talc.
• Stains work well with this glaze but test or check that their maturation temperature corresponds with your firing temperature.

Glaze Trials

Glaze Trials

 

DeBoos Wonder Glaze trials

DeBoos Wonder Glaze trials

General observation: Colourant seemed to spread evenly throughout the glaze. No cracks, dunting etc. Consistent, pleasing, glossy glaze.

Last word – your core artistic endeavour

When venturing into the land of teapots and plates and vases, this article ponders what might influence your glaze choices. Either making to sell or to give to somebody else, prompts consideration of a set of criteria you need to deliver your outcome. (I refer you again to the linked decision tree). A final thought to consider as well (perhaps foremost), is forsaking your own aesthetic as needed in favour of your client’s tastes. Are you willing to go there? Does the vocabulary of your artistic expression fit suitably alongside your functional ware criteria and is this sufficiently satisfying for you? Does this pay the bills? Perhaps a maker/client collaborative model like MudRock’s is the way forward. Alternatively, make like British potter Daniel Smith{21} does. He has consistently used the same glaze for his functional ware for much of his professional making life. With this consistent focus, no wonder it looks so good and sells like hot cakes.

Daniel Smith, UK, nest of bowls, largest diam.39cm

Daniel Smith, UK, nest of bowls, largest diam.39cm

Working with a new glaze

The tried and true method of working with a new glaze is first to conduct trials. A systematic approach to discovering the multiple possibilities of any one glaze is well documented in Greg Daly’s international bestseller Glazes and Glazing Techniques. Greg demonstrates basic and advanced methods of examining a glaze so the artist can make an informed decision of what might be appropriate for the work at hand. Key points are ‘document, document and document’ and be methodical; temper your expectations; be prepared to have dud trials and document these so you learn from them.

Once you have found a glaze to your liking and there is a pleasing aesthetic fit to your work (not all glazes ‘fit’ all styles of work), be sure to record the particulars of your glaze, your fired result, and thoughts for further investigation. One such record keeping document can be accessed, downloaded and printed from the JAC’s website, www.australianceramics.com/journal/glazerecordtemplate

Suggested resources

JAC online resources – glaze record template:
•    www.australianceramics.com/journal/glazerecordtemplate

Web resources

•    www.ceramicartsdaily.org
•    www.ceramicsrecipes.org
•    Material Data Safety Sheets – www.msds.com/

Bibliography

Notes for Potters in Australia, Vol. 1 Raw Materials and Clay Bodies. Ivan McMeekin. NSW University Press Ltd, 1967.
Glazes and Glazing Techniques – a glaze journey, Greg Daly, A & C Black Pub, 2003, ISBN 0713642769
Glazes for Australian Potters, Janet DeBoos, Cassell Australia. 1978, ISBN 0726922129
‘Living dangerously: barium glaze research project’, J. DeBoos, British Ceramic Transactions. 1999. Vol 98, No 1, pp 35–38.
Note: also reprinted in Ceramics Technical with slight alterations – issue reference unavailable.
Digitalfire Reference Database. Technical Articles: Are your glazes food safe or are they leachable?
https://digitalfire.com/4sight/education/are_your_glazes_food_safe_or_are_they_leachable_12.html

Thank you to Val Gordon and Tony Martin for your assistance with content ideas and technical details.
Thank you Janet DeBoos – always generous.

1 https://en.wikipedia.org/wiki/Venus_of_Doln%C3%AD_Věstonice
2 Living Dangerously: barium glaze research project. J DeBoos, British Ceramic Transmissions. Vol.98:1 (1999) pp 35-38
3 Material Data Safety Sheets, www.msds.com
4 Digitalfire Reference Database, (Technical Articles), ‘Are your glazes food safe or are they leachable?
5 Notes for Potters in Australia, Vol. 1. Raw Materials and Clay Bodies. Ivan McMeekin. NSW University Press Ltd, 1967
6 Prue Venables: www.beavergalleries.com.au
7 Mud Rock ceramics, Singapore, www.mudrockceramics.com
8 https://www.tripadvisor.com.au/ Bennelong Restaurant/ Images
9 https://digitalfire.com/4sight/education/what_determines_a_glazes_firing_temperature_201.html
10–20 Glazes for Australian Potters, J. DeBoos, Page 47, Glaze #52. Cassell Australia, 1978
21 Daniel Smith Ceramics, www.danielsmith-ceramics.com