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