Rock Glaze

I have started to get out and collect some rocks, but because of the COVID19 lock-down, I can’t go driving all around my shire doing a full geology excursion.I’m suppose to stay within 5 kms of home. I can go to the shops or Post Office for essentials, but we don’t have a shop or a post office here in our little hamlet.  So we have to go the 5km to the next village where there is a small shop and Post Office. Luckily for me, I have walked all this country around here over the past 45 years. So I know where to go within 5 kms to get some glaze stones. There is a small volcanic plug just a couple of kms away, but it is completely kaolinised and has lost most of its alkali, so doesn’t melt very well – in fact not at all. Also, the high levels of iron and magnesia that are left limit what can be made from it. It’s really just a brown soil and is only good as an iron pigment.It would be nice if there were some acid rocks nearby, but there aren’t. So I’m stuck with what is here. There are just 3 volcanic plugs within the 5 k limit around here. All basalts.


I called in at Werner’s house, just a couple of kms further along, on the way to the shops. Keeping my distance of several metres, I reminded him that I had called in there 20 years ago and he let me collect some of the basalt rocks that out crop from a small volcanic plug in his back yard. Werner is a very nice guy. He has retired since I was there last. We went for a well distanced walk around to his back yard. We are both double vaxed, so felt safe to do so.



Mid last century, this was a working quarry, it’s abandoned and quite over grown now, but there are lots of little, hand-sized, small stones that I can pick up from the garden bed near the top of the quarry wall. I can fit about 15 kgs in my back pack and thank Werner and prepare to walk back out. I tell him that I’ll be back for some more stones in another 20 years! He laughs, he will be 100 by then.



I put the stones through my rock crushers. First, I put the fist sized pieces through the jaw crusher to reduce the stones down to blue metal sized pieces.


Then they go through the disc disintegrator mill to reduce the gravel to grit.


I have installed a flexible dust extractor system that sucks the dust from the machine out through a fan installed in a sheet of plywood that fits in the roller door space. It is quick to install and remove afterwards. This was the quickest and cheapest DIY solution to the OH&S dust problem involved in crushing rocks, as i had the sheet of plywood left over from the ceiling of the throwing room.


I sieve out all the over-sized bits, and put the rest into the ball mill. This reduces the grit down to dust that I can use to make a glaze.I know from my previous research that I can make a tea-dust and a tenmoku glaze from this dark rock. Basalt isn’t very easy to work with, as it doesn’t contain sufficient silica or flux to melt properly. It also has far too much Magnesia and iron to make anything other than dark glazes like tea-dust and tenmoku. Even then, it needs extra limestone and silica to get any usable, stable, glossy result at all. But the thing is, it can be done with a little bit of chemical jiggery-pokery using just what is available around here. In fact. It can be done with what is in my back yard!
My initial test tile showed me that I can make a honey brown glaze, a black tenmoku, a green magnesia matt, a tea-dust green/black glaze and an opalescent dark blue/green glaze.



Meanwhile, Janine is at work making larger bowls on the ’Slatcher’ kick wheel.


While the ball mill runs, I spend a bit of time making some new fibre cement pot boards. I use our own sawn and milled pine slats to reinforce and support the fibre cement sheet boards. Some of the advantages of the FC pot boards is that they are cheap, very flat, quite absorbent and light weight.




I made a couple of stillages on castors to hold the pot boards in a compact and movable form. The first set I made from leftover parts of the brickies’ scaffolding. I don’t like to see waste, so i kept the parts after i dismantled the scaffolding. The other set I made from steel, half of which was left over from the shelves and benches that I made for the Gallery and lab rooms. These shelving racks can hold 28 pot boards if they ever get filled. More than enough for us.


Now that we finally have a continuous, flat, level floor, we can wheel our work between the throwing room, kiln room and glazing rooms as needed. So easy and convenient now. What a luxury!

Dark Chocolate and Dark Clay Pigment

Last week, on the coldest, rainy and blusterously windy day, we had a half day off, lit the stove in the kitchen after lunch, and stayed inside and cooked.Janine made a ginger parkin cake in her very special Swiss expanding cake tin. This was a gift from Barbara, a potter in Switzerland when we were working there some years ago. It had been handed down in her family for some years. Barbara had cooked a cake in it and brought it along to the wood firing workshop that we were doing. I was so taken by its ingenious simplicity, I studied it and even did a drawing of it with the details and dimentions, so that I could make a copy of it for us on our return. I have learnt some very basic skill in sheet metal working. Barbara saw that I was taken by it, with me coming back to it several times and examining it and photographing it.At the conclusion of the workshop it was presented to me gift wrapped. I was really touched. I am still really impressed with this cake tin every time it comes out and Janine bakes in it. Most of all I still recall Barbara, Catherine, Stefan, Eric and the others, up in the Swiss Alps and the great time that we all had together. It brings back strong memories and feelings of good times. It’s a loaf shaped cake tin, but it has a madeleine effect.


This two piece cake tin concertinas inside itself, so it is always the perfect size for almost any size recipe.
While Janine was making her cake, I roasted hazelnuts under the grill, just enought to bring out a little colour and that amazing smell and flavour.We had spent the few nights prior in front of the idiot box shelling the nuts. I melted 2 blocks of cheap, no-frills, German, organic, supermarket 70% dark chocolate in a double boiler, made from a bowl suspended in a source pan of boiling water, I mixed the nuts into the melted chocolate, then poured the mass out into a square cake tin to cool. It is so amazingly delicious, tasty and fragrant, but not sweet, just nutty, melt in your mouth smooth, but with that special freshly roasted hazelnit crunch. Wow! We may not have any money, but we live a rich life. Imagine trying to buy this at DJ’s food hall?


It goes very nicely with coffee.



In the afternoon we made marmalade. A lovely, relaxing and rewarding way to spend a miserable day in the warm kitchen.


The next day, back in the pottery, I retrieved the anvil that had been through the fire and then sat out in the yard for 21 months waiting for some TLC.It should have been rescued much earlier, but I’m working to my limit and I don’t want to overdo it. I can’t do everything. So now is the time to retrieve the anvil. It is the worse for the weather even though I had it tarped, but fire does strange things to iron, and it rusts so much faster than if it had just be put outside. I cleaned a lot of flakey rust off the surface and then treated it with rust converter to stabbilise it. I remember when I bought it back in the 70’s, at an auction for $110. I was so much younger and I could lift it into the VW beetle back then to bring it home.I must have been mad! It’s somewhere around 100 kilos, if not more. I can’t lift it now!I had to use the little crane on my truck to pick it up, and then build a tripod and use a chain block to lift it onto its new block. It’s a thing of beauty and a joy forever! This anvil has an English maker’s stamp on it. I imagine, sometime in the 1800’s?



I cleaned all the loose scale off the surface and swept it up to use as an iron pigment in the future. I read somewhere that Hamada had said that blacksmith’s iron scale made the best iron pigment. I’ll give this a go. I’ll have to calcine it, crush it and grind it very finely first.



I have decided that the best way to use the small ball mill roller is to use it to make pigments. I have done a few experiments with it this week and found that as it overheated and shut down with the 4 litre jar that it came with. I tried my 1 litre jar and also added a small desk top fan to cool the motor. This was the combination that worked well enough, so that it can run for a few hours without over heating and shutting down. I made up a batch of a cobalt pigment that I developed over 40 years ago, just after I left Art School. It has a softer more ‘natural’ look, more like ‘gosu’, with an iron break where it is thicker. We used this recipe for 20 years until I found our local natural cobalt bearing stone.



Recipe;

Red basaltic soil 66%. – Red top soil is high in iron and silica and fuses readily.

Potash felspar 33%   –  The felspar helps to melt it into the surface of the glaze.

Cobalt oxide 1%   – cobalt oxide is such a very very strong colorant, you only need a very small amount.


Cobalt is far too strong to use straight as an oxide. It is also rather grainy and spotty. It needs to be ‘watered down’ with something else to soften it out a bit and dilute it. I have read some pretty exotic recipies that use zinc and tin and manganese, nearly always iron and some with bone ash. 
Michael Cardew recomended a mix of;

Cobalt carbonate 20%

White Tin Oxide 20%

Black manganese oxide 10%

Plastic red clay 15%

China clay 20%

red iron oxide 5%

I tried this recipe when I was a student at Art School, but didn’t like it. A bit too much like fountain pen ink.
My local red clay and cobalt recipe is simplier and it’s mine. It also has that lovely blue/black cobalt and iron break between thick and thin.

I found a deposit of natural cobalt south of here 15 years ago. It was a mix of silica, iron, manganese and only just a miniscule amount of cobalt, but it showed a pale blue when disolved onto a glaze as a brush stroke.
I have always had an interest in fossiking for local materials, processing them and intergrating them into my work. As you can see below, I tested 90 different samples of precipitates from chalybeate springs in the area of my research around here, both active and ancient and dried out and solid stone-like deposits. Numbers 84, 86 and 88. showed a blue colour. Interestingly, the top row were fired in reduction atmosphere and were definitely blue with the cobalt showing clearly.The bottom row were fired in oxidation and the cobalt blue is diluted by the manganese showing a paler grey, purple/mauve blue.Sample number 90 appears to contain mainly manganese and iron with very little cobalt present, being a pale brownish, claret/mauve colour.


My samples averaged;

Silica 55%

Iron Oxide 1%

Manganese Oxide 16%

Cobalt oxide 1%

This equates to something like the ancient Chinese and/or Japanese ‘Gosu’ or ‘Smalt’ natural cobalt bearing pigment stones.
If nothing else, I learnt that I must always test everything in both oxidation and reduction to get a true undersanding of what is going on.

Tragically, I lost nearly all my aged porcelain stone bodies, pigments, ores and minerals in the fire, and now many of the places that I used to fossick are now sterilised by housing developments. It’s going to be a different life now, with reduced access to the minerals that I used to use. We’ll develop a more restrained and refined palette.
So I’m back to milling up a red soil and cobalt mixture to mimic the natural pigment that we used to use.



To make a glaze for my porcelain tests, I have collected and spread out to dry, some of my porcelain clay turnings in the window. I will calcine these and use them as a glaze material too. When blended with Moss Vale limestone, they will melt into a very pale, limpid porcelain glaze. – I hope!
So much to do and so little time.

Ball mills

Janine made up our first bucket of glaze. She mixed up a 5 kg bucket of Leach’s Cone 8 glaze. We have used this glaze all our life. It is the reliable go-to glaze for testing all our clay bodies. A basic and reliable, no frills glaze that fits right in the middle of the spectrum. A great way to compare the various different clay bodies glaze fit characteristics in our first few firings, which will be nearly all tests.

It can also be an extremely beautiful glaze, a pearly, creamy white, surface. But this is only really true if it is fired just to cone 8 only and not higher. We also ball mill the glaze batch for a little while to get all the particles well mixed. Not too long, otherwise the already finely milled felspar granules will start to break down, releasing its alkalis into solution. Felspar does not have a chemically robust structure, so care is advised when ball milling rocks for glazing. To avoid this damage, I usually ball mill my stones dry after putting them through the rock crushers. I can then store the powder for use in making clay body or glazes, weighing them out accurately dry before wetting them down. The alkali is less likely to be released during dry milling.

I’m not trained or qualified in any way to do with mineral processing, but I have worked with locally found stones for my glazes for the past 47 years. Everything that I have learnt is self taught. I built my first ball mill in 1974. The first year after I graduated and I have built a few more since then. I will probably make another one in the coming years, when time permits. I have always kept a ball mill log to track my ball mill usage. I kept a record of what was milled, for how long and how much was in the mill, wet or dry milling and the date that I milled it, as well as any recipe involved. I lost that log book and all my other glaze recipe books etc. in the fire. Just as I did in the first and 2nd fires. I had two copies of my glaze recipe books, one in each building, but they both burnt down! I can remember that my most recent milling log, kept since 1984, I had clicked up over more than 1,000 hours of milling since then. but the exact number escapes me now. Somewhere around 1050 hours? With an average milling time of 2 to 3 hours, This is about 500 uses of that last mill. Thats a lot of hours of loading, unloading and washing out.

My friends have sourced some 2nd hand ball milling machines for me. Len Smith is always on the digital lookout for me for bits of equipment. He is so fantastically resourceful! He told me about a deceased estate of a potter. I turned up (before lock-down) and was lucky to buy what appears to be a locally made copy of a Shimpo ball mill roller and two 1 gallon, Chinese made porcelain jars. One was broken on the shoulder near the locking stud and the other has a brittle, seized rubber ring seal. Was able to prize the stuck lid off with a chisel. They both need some work. But I was lucky to get them. I made a new silicon rubber seal for the seized and a flat rubber washer type of seal for the other.

I vaselined the ground porcelain jar rim, then extruded a thick silicone rubber ring around the lid and placed it on the jar overnight to set.

This has created a new, soft and springy rubber seal that will keep it going for another 30 years.

My friend Simon Bowley, just gave me his 3rd hand Shimpo mill roller and a beautiful 15 litre Chinese jar. It has the brass wing nut and brass washers missing to secure the lid. This gadget was stored in an old shed for some years, and I’m not too sure if it has ever been used very much. As it still had the paper label from the supplier (Walkers) glued to the outside of the jar. This started to wear off as soon as I used it.

I made a couple of brass washers from the ‘hole’ pieces that I cut from the pottery sink splash-back to get the water pipes into the shed.

I hadn’t thrown them out, as I thought that they might just turn out to be useful some day. A good piece of thick brass like that, 6mm thick is too good to throw away! They came out of the hole saw pretty rough, but I was able to file them down to a smoother finish and drill out the centre hole to a clearance on 3/8″ BSW thread and they work a treat. Not many potters have the luxury of solid 6mm brass washers on their mill jar.

Len also located a very small ball mill unit in Melbourne that wasn’t being used and was able to be donated to me as a bush fire victim. It looked as though it had hardly ever seen the light of day. It came with 2 beautiful Daulton porcelain jars of about I gallon, or 4 litres, and a plastic bucket of small milling media to suit. The jars had some remnant brown dust in them, but looked as though they hadn’t been used very much.

When I tested the small mill roller with one of its Daulton jars loaded with balls and water to clean the mill. I found that the motor overheated and stopped after 25 mins. I can see why this machine wasn’t used very much. It doesn’t work! 30 mins is only long enough to do a bit of blunging, but a couple litres isn’t enough to achieve much. I will need to change the motor for a larger/stronger one. These Daulton jars will fit on the smaller end of Simons mill roller, so I can use them in this way.

My friend Tony Flynn gave me his shimpo potters wheel a few months ago, He also gave me a tiny 1 litre porcelain jar. This could be useful for milling pigments. I tried it on the RMIT roller the next day and it was small enough and light enough not to over heat the motor. It got too hot to touch, but didn’t trip the overload switch. so this will be a useful combination for small batches of pigment.

So now I have a 3 different jar roller mechanisms and by mixing and matching the different jars, I can use the Daulton jars on Simons roller, Tony’s jar on the small roller, Simons big jar on his roller and one of the smaller Chinese jars on the deceased estate roller.

Most of the jars needed new rubber seals. I had already been to the tyre business in Bowral and asked for a punctured inner tube from their rubbish bin, so I was prepared.

All the jars needed to be washed out and cleaned, then filling with balls and water and run for an hour or so the get the surface of the balls and mill all clean and fresh to start work. After milling like this the water turns cloudy, so the balls are rinsed in 2 buckets of fresh water, then placed in a plastic garden sieve to drain and dry out.

The volume of all these small jars added together just about equals the one bigger 25 litre jar that i used to own. The big difference is that to load all 5 seperate jars, run them on 3 different machines and then clean them is a lot of extra time and labour. But at least I can get some stones milled and local rock glazes made to get us going.

I stopped off at a few local sites on the way to the supermarket a few days ago. So I have a few bags of stones to work on. The next step will be to get the rock crushers going. The roller mill is still in pieces and needs some TLC