Monday, January 18, 2010

Crystal glaze:Lasse Östman:A Painting in Progress:Barry Brickell:My Uncle and Aunt:Live cat shipment

Cobalt oxide coloured crystals on pale copper green background.
(lustre en cristal de poterie L'oxyde de cobalt a coloré des cristaux sur le fond de cuivre pâle)

I was looking for something to do with my old electric kiln, and thought I would try some crystal glazes. I have not seen many examples of crystal glazes in "real life", a couple of dusty examples in a second hand shop a few years ago, and a small vase that a friend has, is about my sum total.

Pale copper green background surrounding peachy tan crystals.

I have done quite a lot of reading about crystal glazes recently, and, of course, have spent rather a lot of time on the Internet looking at examples. To be honest, most leave me a bit cold. I guess I am still a bit of an ape man with long hairy arms, and knuckles that drag on the ground when it comes to pretty pots, but...... some of what I saw interested me a lot, both from a technical point of view, and from an aesthetic one.

Cobalt oxide coloured crystals with orange/yellow background.

One potter that ticks both of those boxes for me is Lasse Östman, a Swedish potter. He seems to approach the whole matter of growing crystals in glazes, and sharing information with common sense and generosity. To help me get started in what was clearly going to be a long and adventurous journey, I began by testing some of his recipes. Some worked really well, straight out of the box, and others were promising. Then, in a second firing, I started building a wider palette of colours by trying out different metal oxides, and I tested more of his base recipes.

Crystals in a bowl. Notice bronze colour where glaze is thinnest near the rim of the bowl, then blue crystals in the thicker glaze. Right in the bottom of the bowl the crystals are organized differently in the thick pool of glaze, and do not reflect back the blue colour.

Progress thus far has been very encouraging. Of course I like to make things difficult by also experimenting with the firing schedule, and that is part of learning!

Cobalt oxide crystals on graduated pale brown to yellow background. Colouring metal oxides seem to concentrate in the crystals, and the background colour is that of the base glaze. A good use for a defective bisque fired mug!

I have tested glazes on some bisqued mugs that had some minor faults. These have proved very useful test pieces for the glazes, giving a slightly curvaceous near vertical profile which allows the glaze to flow and pool. In general, crystal glazes are, and have to be, rather runny by nature. Also glaze thickness has a big effect on how readily crystals will form in the glaze.

Cobalt crystals over a mostly copper coloured background. This little pot is 6 inches high (150mm)

Most of my test pieces are fired on little pads made from a circle of insulating fire brick. This is sat in a little bowl, and everything is thickly coated with alumina hydrate and a touch of ball clay to hold the alumina together. The idea is that the bowl catches any spills from the fluid glaze, and the pad of insulating fire brick is easy to grind off the pot if it gets stuck with glaze. The system seems to work well so far.

Glaze catcher at work, and doing a good job!

Glaze is really a special sort of glass, and glass has no crystal structure, its molecules are not arranged in regular patterns, and light tends to pass right through it because of this. In certain circumstances, however, it is possible for structures to form within this "primordial gloop"! The glazes I have been playing with are very high in zinc, around 18 - 19 percent by weight, and the crystal structures that are forming in the glaze are zinc silicate. The formulation for a 1250 Centigrade (2282F) is very similar to a glaze that would mature at 1060 Centigrade (1940F). When it is heated "seeds" form in the glaze that are potential crystals. At top temperature the glaze flows and some "seeds" are lost. After a holding time at top temperature, the usual procedure is to cool the kiln by about 150 Centigrade (320F), and then hold that temperature from anything from 30 minutes to several hours. At this temperature the seeds accumulate more and more material from the glaze and crystal structures form. The longer the temperature remains here, the larger the crystals grow. Then the kiln is allowed to cool normally. There are variations on this method, Lasse Östman usually holds the kiln at top temperature from 30 minutes to 1 hour, then cools normally.

Lots of testing has to be done as the cooling characteristics of individual kilns vary, as do glaze materials, and the clay that the pot is made of. In both my test firings I introduced a crystal growing period at 1100 Centigrade (2012F), and made this longer in the second test to try to understand the relationship between time at crystal growing temperature and the size of crystal. Currently I am growing crystals that average about 2 cm with an hour spent at 1100 Centigrade (2012F).

Needless to say, not everything turned out "successfully" in the sense of something beautiful happening. Some glazes were sugary and under fired in this firing, and some were put on too thin. But all tests yielded very useful information, and more will be done soon.

Laura is painting a lovely large picture at the moment, and I thought it would be nice to have a photo of her at work here, as her blog hasn't been updated for such a long time.

Detail of the painting as it progresses.

Laura deep in thought. She always works with her paintings flat on the table.... I don't know how she does it, I always used easels myself!

We both went to an exhibition of Barry Brickell's pottery in at Brett McDowell Gallery in Dunedin last week. It was so refreshing to see robust and humorous forms, juicy salt glazing, and groggy clay. Barry is a very well respected New Zealand Potter who has his pottery (and railway) at Driving Creek, Coromandel.

Sculpture by Barry Brickell.

Fatso Jug, by Barry Brickell


My Uncle and I sharing a laugh... not sure if my Aunt knew what was going on behind her!
(Mon oncle et tante d'Australie. Mon oncle et moi partagent une plaisanterie.)


A recent special treat has been a visit from my Uncle and Aunt from Australia. It was lovely to have time with them, to enjoy fun and good chats around the table. Truly time to be treasured.

NZ was once famous for live sheep exports, now for something smaller! They say that Ginger is good for the digestion! OK... all in bad taste, but Ginger does look cute in his box. When he bothers to be awake, from the comfort of his box Ginger watches the cars go by on the main road... and the sparrows hopping on the pavement!

(Gingembre le chat. Délicieux ! Si endormi il rêve des oiseaux et des souris ! Il regarde si gentil dans sa boîte.)

12 comments:

Hannah said...

Hi Peter, you've made a great start with those glazes. There are a few folk doing them over here but the forms always seem to be the same that they put them on, maybe that's purely because of how they work best, I'm not sure.
Love the ginger cat, he's a beauty.
Have you been up to Barry Brickell's place? It's fab, we went - of course! Can't remember if I told you that the film about it was made by my relative up in Auckland, Lynton Diggle, oh did they manage to call in on you? Not sure if they are still away. I think they may still be in mid holiday yet. Hope they do manage to come and say hi.
h

Peter said...

Hi Hannah,
You must be sitting in front of your glowing screen at the same moment that I am sitting in front of mine. I was just rechecking my mail and catching up on reading a blog when your comment popped up! Fun isn't it!

Mmmm, crystal glazes, if I get much further with them I would love to find a way of using them with other glazes on something sculptural, maybe undulating forms that allows the glaze to pull and pool. A year or two ago I did see a really "grunty" looking huge platter that someone did that had gloopy thick glazes and some areas that had crystals, it was all rather refreshing, and gave some hints that more is possible with crystal glazes, it just needs imagination and some daring!

We visited Barry Brickell's place two years ago and greatly enjoyed looking around the kilns, his sculptural pieces that were dotted around the place, and the railway.

Haven't seen your relatives yet, but would love it if they call in. They really should visit this part of NZ with its Scottish heritage!
Anyway, nice to hear from you. Stay warm!

Ron said...

Looks like you've got the knack for growing those glaze crystals.

Linda Starr said...

Oh Peter, your posts are chock full of information, I love laura's new painting with the butterflies. the sculpture of barry brickel is awesome and you have amazed me, but maybe not on your crystal exploration, good going on those.

Armelle said...

Hello Peter,

Your crystal glazes are really beautiful, yet it leaves me cold too, at first. I cast a glance at the formulas Lasse Ostman and it calls for temperatures of 1260 °, I admire you can convert them to 1100 °.
I am still awaiting my electric kiln, it's almost like a gift, my supplier makes me wait, I look good. Looking for recipes for glazes earthenware for cooking in the vicinity of 1060 °, I came across one of your articles. I can not find recipes in French on the internet and the book I want is exhausted. But when I look at the list of materials to achieve the glazes from my supplier, many ingredients miss or may have a different name, especially the fritts.
All my encouragements for your crystallization, much like the second (pale copper green background surrounding peachy tan crystals) and also to Laura for this painting, hello to Ginger.

Bonne soirée

Peter said...

Hi Ron,
Early days yet, but a good start thanks to Lasse Östman.

Hi Linda,
Lovely to see Laura's painting in progress, it is much more beautiful in real life than in the photo. Barry Brickell's work at the exhibition was very refreshing and full of life.

Bonjour Armelle,
Regarding Lasse Östman's formulas, I have probably confused you. I do still heat the kiln to about 1260 Centigrade, then cool to 1100 and keep at that temperature for up to one hour. After that I let the kiln cool naturally.

Regarding recipes for earthenware glazes, the good news is that there are lots of simple ones for 1060 Centigrade. I can give you some recipes, and I am sure that some of the other potters that read this would be happy to help you too.

Does your supplier have a web site? If so, can you tell me what it is, and I can see what materials you have available to you? I might be able to understand enough to help.

Au revoir!

Armelle said...

Hi Peter, I understand now how crystal glazes works.

Thank you for your help. It's not hurry at all.

A bientôt

mudheartpottery said...

Hi Peter,
Happy New Year to both you and Laura. Clay has taken a back seat but I am determined to get my hands dirty soon. I still check on what everyone else is up to and I will join you all soon!

Peter said...

Hi Armelle,
Glad that made things clearer! I am firing another test of crystal glazes at the moment. It will be interesting to see the result.

Nice to hear from you Lyn, looking forward to seeing what your "dirty" hands produce!

Jewels said...

Hello Peter! Wow! You are getting some amazing crystals to form! They are beautiful and magical – like frost on a window. I have never seen crystal glazes on a bowl before. Is that because the shape is not conducive to the crystals forming (due to pooling) or because it isn’t a food safe glaze? The fire brick would make grinding off the glaze much easier – nice tip. Laura’s painting is mesmerizing – like stepping into a marvelous dream! I love it! Not sure Ginger would be good for digestion, but he is certainly good for the heart! You three take good care!

cindy shake said...

I'm with you Peter on the crystal glazes -however the blue does remind me of some of our frosted windows here in Alaskaland! I like your idea of the glaze catcher bowl and your wife's butterflies are BEAUTIFUL! I also like to paint flat -my depth perception was always a bit skewed when I paint or draw vertically ;o)

Peter said...

Thank you Jewels and Cindy for your Comments which came through as I was putting together my next post. Lovely to hear from you both. Regarding crystals and food safe... I think there could be the potential for heavy metal release, because the crystals seem to concentrate such things as cobalt (notice the dark blue crystals and yellow background), so I would tend to make less functional forms, however a bowl used for dry food such as nuts and so on would be OK I am sure.
Hi Cindy, goodness... another painter on the flat! I find I get things out of kilter with proportions that way, but some wet in wet things work nicely like that. I don't know how old Mike managed the Sistine Chapel ceiling... he had the opposite challenge of painting whilst on his back looking upward! It makes life more fun that we are all different :)