Monday, February 8, 2010

Glaze testing part 1. Some more crystal photos.

I am going to take a bigger risk than ever over the next few posts, of looking even more foolish than I usually do! I am going to write a little series about testing glazes. It isn't going to be technical, it will be more like cooking. I hope it will help some people.

When I started potting, not all that long ago, I read lots of pottery books and magazines, and took a real interest in glaze recipes. There were recipes that sounded like they would solve my deepest desire and need. Wide temperature range glazes that would provide superb results from Cone 01 to Cone 10! Never craze recipes for domestic ware. Clear gloss, satin, mutton fat, and shino, they were all there for the taking! I bought lots of materials, and many tested dozens of glazes, always with the highest hopes, and usually my hopes were dashed!

I discovered that the glaze that you make from someone else's recipe, is almost certain to behave differently than the original, this is because our raw materials, kilns, and clays are different. You are also likely to apply glazes in your own individual way!

The good thing is, that sometimes other people's recipes will work, but ... the reality is that you will have to test glazes to be sure that they will work for you.

Chances are that the fiddly bits of this and that in many glazes that you might see were put in by the author of the glaze to make it work for the clay they used and the materials that they had available. There are times when it is better to start from scratch, and make something for your own clay and kiln. But where to start? That is the question!

Making a simple lead free glaze for earthenware (Part 1)

Making something to test glazes on.
The first job is to prepare something to test glazes on. Use the same clay that you make pots out of to make the test pieces. It is also useful to make them about the same thickness as your usual pots.

I have used small bowls, flat tiles, and other shapes to test glazes on, but I think that the following shape probably gives the most useful amount of information.

First I weigh out about 1.8 kg (4 pounds) of clay. I form it into a thick walled bottomless cylinder about 230mm (9 inches) in diameter. I leave a little step of clay on the inside of the cylinder approximately 1.25 inches (30mm) wide.

I pull up the clay to 100mm ( 4 inches) high and form a little step on the outside of the cylinder as I do.

You may find that there is enough clay to go a lot higher than this (I did), and you may need to pull higher to make the thickness of the cylinder like that of your usual pots. If this is the case, pull the cylinder higher, but trim it with a needle to a height of 100mm (4 inches).

The final cylinder is about 200mm (8 inches) in diameter not including the extra width of the step. Finish the cylinder by making some ridges and grooves with your fingers or a wooden tool inside and outside. These will help determine if the glaze will change colour nicely when it goes over ridges and grooves on an actual pot, or if it will obscure detail.

Make some white slip. 100 percent ball clay will do just fine, but......
I use 90 parts ball clay to 10 parts medium borax fritt (4124, or 3124). I find that the fritt does help the ball clay adhere to the pot when it is fired, and seems happy right through the temperature range from earthenware to stoneware; other borax fritts can be substituted.

My slip was 900 gm ball clay
100 gm fritt 4124
1750 ml water

First put about 1000 ml of water into a container, then add the dry ingredients. I mix these in with a paint stirring attachment to the electric drill. Once the dry ingredients are mixed in to what will be like whipped cream, then add the rest of the water progressively until the slip becomes a nice thick brush-able consistency. If your slip is lumpy, you may need to sieve it..., you probably should sieve it, but my electric paint stirrer is sooo good, that I didn't find that necessary.... lucky me!

On a banding wheel, paint white slip on the outside of the cylinder with a soft brush. Do not paint the inside.

Paint the cylinder down to the step.

Now measure equal portions around the cylinder. I calculated that a 200mm (8 inch) diameter cylinder should divide nicely into 50mm (2 inch) portions.... and they did on mine!
I lightly pressed vertical marks into the slip to help me with the next task...

With a wire or thread, cut right through the cylinder at each 50mm (2 inch) mark. Like cutting a cake!

There we have it! When the clay has dried overnight I will be able to separate the pieces, and put them on my drying rack to dry completely. Each piece of the "cake" should be able to stand up by itself, which is why we made the inside and outside step.

Crystal glaze.... beautiful, but is that enough? (Lustre en cristal…. est-ce que beau, mais qu'asse'est ? "Mmmm, intéressant…, mais pour quoi pouvez-vous l'employer ?" )

Below are some new examples of crystal glazed pots that I fired last week. I am pleased with progress, although I don't know how well they will sell around here. The most frequent comment I have had so far has been "Mmmm, interesting..., but what can you use it for? That narrow neck..., I suppose you could use it for a single flower..., maybe?"

Is it wrong to marvel at the dew on a spider's web in the still of the early morning?
Can it be so wrong to lift the arms and dance like a bird when a warm breeze says "you must!".

Je danse dans le vent !
Je ris au soleil !
Comme une plume mon esprit volera !

Just a thought!

190mm (7.5 inches) high


165mm (6.5 inches) high
the crystals were pale green up top and blue down the bottom of this

125mm (5 inches) high

detail, notice dark outlines

165 mm (6.5 inches) high

detail, the crystals were up to 30mm on this one

150mm (6 inches) high

detail, notice "runs" and thin dark outlines

190mm (7.5 inches) high


Linda Starr said...

Great tutorial, love the crystals that have lots of space around them and the bottom pot is wonderful, boy you are really getting such fabulous results.

Angie said...

This is a very interesting idea with it.Looking forward to the next chapter.

I know it is great that an beautiful item has a use but surely these recent pots are works of art be looked at and enjoyed ...does a sculpture or painting have a use other than bringing pleasure and food for thought, to the beholder.

cindy shake said...

Peter, this is my kind of testing! You do the tests and I get to read and see the results!! This will be wonderful, your expertise will be much appreciated :o)

Amy said...

what can one use those pots for?
of course, to look at! :) they're simply beautiful.

rwhendrix said...

Beautiful big blue crystals! But why do you make the neck on the pots so narrow?

Peter said...

Hi Linda, Angie and Cindy,
Glad you are enjoying the tutorial, I realized at about 4.30 this morning that my tutorial was already sounding biased towards those who make pots on a potter's wheel, and I should have given an example of a glaze test tile as well for those who hand build, but I guess people will figure out that I am after a tile that is 4 inches tall by 2 inches wide (100mm x 50mm), and will stand up in the kiln on a simple base.

Cindy, tut, tut... this is to encourage everyone to do some testing! :} But hope it does help.... I hope I manage to get a glaze or two out of it that I like too!

The Crystals.... Happy to report that I sold one today to someone really nice who began by asking... "are they OK to put flowers in, they have such narrow tops?"

Richard asks "why do you make the neck on the pots so narrow?" and it is a good question.

I guess the first thing is I made them that way because I like the shape, I like the flow from neck to shoulder that the narrow neck gives, and I like the roundness of the form.

Another thing going on is that I am making something that is deliberately not very useful (that sounds daft I know!) I hope that its uselessness will help the pots be seen as sculpture, or just enjoyed for their beauty.

I think Amy has put things rather well in her comment, "what can one use those pots for? of course, to look at!"

One of my favourite trees is the Horse chestnut, my tree book assures me that it is quite useless! The fruit can't be eaten, the timber is not much good for building or cabinet making, and the wood does not burn well. Its only justification for being planted (according to the book) is that it looks beautiful! I think the tree should be adopted by all artists as a "sacred" tree of the arts!

Aude Terrienne said...

Beauty IS useful.
From the beginning of humankind we tryed to make world mor beautiful.
sorry for my bad english.
I like very much your blog, full of nice photos.
Congratulations for your work.

(I am a pupil at clay-work and china painting, from Armelle's blog)

Aude Terrienne said...

I mean I know you from Armelle's blog!

... and I forgot an e at the word "more" !

Peter said...

Bonjour Aude Terrienne,
How good to hear from you. Yesterday I started to read your blog, and am enjoying it, but I had not yet had the courage to leave you a comment, because my bad French is so much worse than your "bad" English! You have good quotations, and I was interested by your thoughts about China.

Best Wishes, P

Armelle said...

Wowwwwwwww........I enjoy, your tutorial, your crystal glazes, the narrow necks of your sculptures.....and the meating between New-zelander and french.............
so nice !!!
Have a nice day Peter,
Bonjour à Laura et Ginger (mine was called "Ruz", it's a britton name and means Red)

Peter said...

Bonjour, Merci vraiment Armelle, de votre encouragement! Il est bon de rencontrer l'Aude Terrienne également. C'est de bonnes gens de réunion tout autour du monde.

Laura dit bonjour. Le Gingembre ronronne (purrs) heureusement! Ruz et la "rust" anglaise de mot doivent être de la même origine.

bonne journée!

Anonymous said...


Peter said...

Hello Dad,
Sorry that you have been having trouble sending comments, I'm glad the Anonymous system works in the mean time.

Anonymous said...

Yes Peter,
Time can be mean - some times- I mean it can go too fast when you're enjoying something, like your beautiful pots and your excellent tutorials, but too slow in the unpleasant happenings of life!
If times had been different you might have become a University Research Fellow - but then your other multifarious talents could have been wasted!

Meanwhile I remain your very very proud Dad!

Peter said...

Thanks Dad!