Tony Ferguson on fri 18 jul 08
Nancy,
How many hours transpired from the time you made the mold to the time you put slip in it?
Tony Ferguson
Nancy Udell wrote: Hi clay buds,
Requesting help from anyone who has knowledge of slip casting and
slip formulation. Decided to try as a summer project making a set of
slip cast dinnerware. I am fairly familiar with plaster, but slip is
new to me. Bought Andrew Martin’s book and made a couple test
molds. So far so good.
Mixed up a test batch of Hensley/Polseno Cone 7 Slip
OM4 25
EPK 18
Tile 6 5
Neph Sy 35
Custer 9
Frit 3110 1
Flint 7
100
water 42
sodium sil .3
I ended up with a slip that will make castings, but does not release
from the mold uniformly – sometimes sticks and cracks – and does not
dry and become solid in a short period of time – 3 or 4 hours or
overnight. The book says that for troubleshooting these problems
could be too much water, too much EPK or not enough defloculant.
A couple questions:
1. Am I adding the right amount of water and sodium sil?
I assumed that because the dry ingredients are by weight, that the
water and sodium sil should also be by weight. The book (while
excellent in many respects) does not make this clear anywhere. I
found the weight of water on the internet, and since water is 42,
added 19 litres (42 pounds). I then converted .3 lbs to grams and
weighed out 113.4 gms of sodium sil on my gram scale.
Is this the right way to do it?
If this is right (i.e. if I have correctly mixed the slip) how do I
know which of the trouble shooting problems to try to correct? I
don’t know how to do this with multiple variables.
We are at 7200 feet altitude here. Can that make a difference?
Thanks for any intelligence you may be able to share.
Nancy Udell
Santa Fe, New Mexico
505.984.9907
www.clayandcolor.net
Tony Ferguson
315 N. Lake Ave. Apt 312
Duluth, MN 55806
...where the sky meets the lake...
Artist, Educator, Photographer, Film Maker, Web Meister
fergyart@yahoo.com
(218) 727-6339
http://www.tonyferguson.net
Terence Nelson on fri 18 jul 08
Nancy,
There is a review of that book on Amazon's website (URL below) that reported the same problem with that recipe.
Generally, the weight of the water in a casting slip should be almost equal to the weight of the dry materials according to Tony Hansen's article (also linked below). I believe the canonical value of the specific gravity is 1.8, which you can measure with a weighted glass tube called a hydrometer.
You may need soda ash with sodium silicate according to the 3rd link. I am deflocculating with Darvan 811, which is supposed to be better for the plaster mold.
terrypotter in nj
http://www.amazon.com/review/R1DOMB6X27NC1DASIN=1600590772&nodeID=
http://ceramic-materials.com/cermat/education/213.html
http://ceramic-materials.com/cermat/material/260.html
Nancy Udell wrote:
Hi clay buds,
Requesting help from anyone who has knowledge of slip casting and
slip formulation. Decided to try as a summer project making a set of
slip cast dinnerware. I am fairly familiar with plaster, but slip is
new to me. Bought Andrew Martin’s book and made a couple test
molds. So far so good.
Mixed up a test batch of Hensley/Polseno Cone 7 Slip
OM4 25
EPK 18
Tile 6 5
Neph Sy 35
Custer 9
Frit 3110 1
Flint 7
100
water 42
sodium sil .3
I ended up with a slip that will make castings, but does not release
from the mold uniformly – sometimes sticks and cracks – and does not
dry and become solid in a short period of time – 3 or 4 hours or
overnight. The book says that for troubleshooting these problems
could be too much water, too much EPK or not enough defloculant.
A couple questions:
1. Am I adding the right amount of water and sodium sil?
I assumed that because the dry ingredients are by weight, that the
water and sodium sil should also be by weight. The book (while
excellent in many respects) does not make this clear anywhere. I
found the weight of water on the internet, and since water is 42,
added 19 litres (42 pounds). I then converted .3 lbs to grams and
weighed out 113.4 gms of sodium sil on my gram scale.
Is this the right way to do it?
If this is right (i.e. if I have correctly mixed the slip) how do I
know which of the trouble shooting problems to try to correct? I
don’t know how to do this with multiple variables.
We are at 7200 feet altitude here. Can that make a difference?
Thanks for any intelligence you may be able to share.
Nancy Udell
Santa Fe, New Mexico
505.984.9907
www.clayandcolor.net
chris1clay on sat 19 jul 08
Hi Nancy,I have taken a workshop with Andrew Martin and also use his
recipe without fail. I use the liquid sodium silicate and weigh it as
if it were just another dry material. It works and is simple. I also
find his test for checking the slip by letting it run over the hand
works great. As for the water, after adding the 40% h20, I mix well
and then pour a small amount on a plaster slab to see if it is as thin
as I want. It not I add more water. Works everytime! Hope this
helpsChristine Laginesschris1clay@yahoo.comwww.etsy.com/shop.php?
user_id=3D5925619
Christine Laginess
chris1clay@yahoo.com
Etsy seller name ChristineLaginess
www.etsy.com/shop.php?user_id=3D5925619
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