Mary and Trevor Mowbray on wed 16 jun 04
Hello potters,
I've been following the postings about the plasticity issue.
The point was made that the older the clay the more plastic it becomes.
That was always my belief too. BUT that is why I wrote to Clayart - I
had clay that was kept for a long time, both damp and dry, and it had
lost plasticity. The only way I could use it was by mixing bentonite=20
and paper into it, and even then only for slab slumping.
Adding "stinky water" didn't help, either - much of the clay was already
"stinky". After reading another thread on Clayart, I considered trying =20
polyethylene glycol - thank you, Michael - and I may yet do that.
However, a friend suggested that vinegar might do the trick, and on a=20
small trial it seemed to help substantially.
About your trip to NZ, Steph : you are welcome to email me for contacts =
in
Wellington, and our Wn Potters' Assn will be pleased to meet you.
The only NZ-er I have seen write to Clayart was Lawrence Ewing and he is
in Dunedin, but I can probably put you in touch with potters in other =
centres.
Regards,
Mary Mowbray
Ron Roy on thu 17 jun 04
Hi Mary,
Some clays contain certain materials that will leach alkalies - Neph Sy
would be one of those materials.
What you have is deflocculated clay - due to alkaline salts probably.
What happens is - the electrical charge on the clay particles changes in a
way that is derogatory to what we call plasticity.
What makes me so sure in this case is that adding vinegar - an acid - is
one way to reverse the problem.
One way of fixing the problem is to add disolved Epsom salts - you will
need to calculate how much free warer is in the clay for starters - weigh 5
lb. wet clay - let it dry - weigh again - you then will know the % of free
water and can calculate how much Epsom salts to add per pug.
The amount of Epsom salts to add is 2 lb. per 1000 lb dry clay - so 0.2 lb
per 100 lb. of dry clay or 0.02 per 10 lb. Just convert lb to grams using
453.6 grams per lb.
Remember to disolve the salts well - in very hot water.
You will need to add extra water because plastic clay needs more - you will
find out how much more when you do it.
I hope you have a pug mill to do the mixing - other wise it is going to be
a difficult job.
Let me know if you need more on this - RR
>I've been following the postings about the plasticity issue.
>The point was made that the older the clay the more plastic it becomes.
>That was always my belief too. BUT that is why I wrote to Clayart - I
>had clay that was kept for a long time, both damp and dry, and it had
>lost plasticity. The only way I could use it was by mixing bentonite
>and paper into it, and even then only for slab slumping.
>Adding "stinky water" didn't help, either - much of the clay was already
>"stinky". After reading another thread on Clayart, I considered trying
>polyethylene glycol - thank you, Michael - and I may yet do that.
>However, a friend suggested that vinegar might do the trick, and on a
>small trial it seemed to help substantially.
>About your trip to NZ, Steph : you are welcome to email me for contacts in
>Wellington, and our Wn Potters' Assn will be pleased to meet you.
>The only NZ-er I have seen write to Clayart was Lawrence Ewing and he is
>in Dunedin, but I can probably put you in touch with potters in other centres.
>Regards,
>Mary Mowbray
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ivor and Olive Lewis on thu 17 jun 04
Dear Mary Mowbray,
An interesting history of your clay. Was this something you compounded
for yourself or was it a commercial product.
For a clay to go "Short" would be unusual if were compounded with a
sufficient quantity of Ball clay, or if the wild stuff, contained a
good proportion of ultrafine Kaolin type clay.
do you have information about its composition?
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
.
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