Wednesday, 8 April 2015

reconstituting used porcelain casting slip

Once upon a time Perth had a ceramic factory in Subiaco. It was founded in 1921 as Calyx Porcelain and Paint company, later changed to Bristile and by the time I became a ceramic student it was known as Australian Fine China. It produced a wonderful white, sturdy (but not translucent) porcelain that we could go and buy by the bucket-loads in slip form, or lengths straight from the pug mill. It was so affordable and abundant even for the student budget that I did not have to be precious with the use of the material. I was free to experiment and play and I created some, to my mind, innovative and challenging forms:  

The factory in Subiaco closed in 2006 and production was moved overseas, to Brazil.
For us it meant no more porcelain slip.
Insert a big "sigh" here.
The consequence for my work was bigger than suspected. I had to find a new material to work with, and although I have tested several brands of porcelain slip, I could never reproduce the results I could achieve with Australian Fine China....and with 11 x higher price, I could not afford to be frivolous with it.

I have saved a few large bags of used, discarded and dried up Australian Fine China porcelain slip to reconstitute later.
As students,we were taught that you can add up to 20% of used slip to the new slip.
I have to reconstitute 100%.
Well, after 7 or so years waiting for the right moment, I have finally decided to give it a go:

First I have soaked dried slip in a bucket of water until it all dissolved. About 24 hours:

Then I have stirred it with my wonderful drill tool. It is a plastic chain ( so that it does not rust) attached with nuts to the length of threaded rod - available from the local hardware shop. It works better than any commercial paint stirrer:

The slip was quite thick, so I added about 5 ml of Dispex to the 3/4 full bucket. 
It was still too thick, so I added a dash (few ml) of Sodium Silicate.
That worked beautifully. When I put my fingers in the slip, and than spread them wide, there is a web of slip between my fingers.
To me that means that the slip is good.
Although it is better to let the slip mature for at least 24 hours, I could not wait so I cast it immediately:

No pinholes, no drips, and it released from the mould beautifully.

The Coral just come out of the kiln.
Welcome back :)

I have to make a batch of them and then all the reserves of Australian Fine China porcelain slip will be gone......
And if you have been told that you can only add 20% of used slip to the new batch, please test it anyway.