Roger Korn on sun 21 apr 02
Ceramic Design Group wrote:
> ...
>
> Sodium silicate and soda ash are very powerful deffloculants and have a
very
> narrow working range and it is very easy to overuse them and render your
> slip thixoid. My suggestion is to use Darvan 811 as it is makes more
stable
> slips with a wider working range.
I gotta' try Darvan. With 1 or 2 gallon slip batches, the soda ash/ sodium
silicate
is very sensitive. You got thick goop, add one more drop, and poof! perfect
viscosity. Then a week later you get out the same slip, its all thick again,
so mix
for ten minutes - sometimes its fine, sometimes you need to add ONE DROP of
deffloculant. If Darvan has a broader range, I gotta' try it.
>
>
> The best range for specific gravities is 1.75 to 1.80 but note that each
> slip has its own unique and best SG. Each slip will also have its own and
> unique viscosity .
I go down to SG = 1.7 when I'm making long stemmed pipes. Draining through
the
stem, I get more even wall thickness with the thinner slip.
>
>
> We have recently been using a #2 Zahn cup to monitor viscosity
I use the case those 55ml syringes come in. Melt a 1/4" OD hole by heating a
drill
bit and fill it up. About 16 seconds is about right. You can get the
syringes at
your drug store. Ian Currie uses them for his grid method volumetrics. GREAT
water
pistol - lube the plunger with vaseline and you can shoot 75 feet easy.
> and a
> Pyknometer for very accurate SG readings.
Wish I had one. A glaze hydrometer gets stuck at that high an SG, and
weighing a
known volumn is tedious.
>
>
> Good luck
Thanks for the input, Jonathan.
Roger
--
Roger Korn
McKay Creek Ceramics
In AZ: PO Box 463
4215 Culpepper Ranch Rd
Rimrock, AZ 86335
928-567-5699 <-
In OR: PO Box 436
31330 NW Pacific Ave.
North Plains, OR 97133
503-647-5464
Mercy Langford on sun 21 apr 02
hi- does any body know if it's possible to make porcelain slip out of
porcelain clay??? I have 25lbs of clay aand a blender and I need to
slipcast
a couple of molds. How much water? any extra chemicals that I would need?
thanks alot in advance-Mercy
Roger Korn on sun 21 apr 02
I can't give you an exact recipe, but here's a procedure that will work.
Mix clay and water into a slip that has a specific gravity between 1.7 and
1.8.
Measure the water you added and record it. This means that a liter of slip
should
weigh between 1700 grams and 1800 grams or, using English units, a pint of
slip
should weigh between 27.2 oz and 28.8 oz.
The slip will probably be too thick to pour. It should be like really thick
cream.
To change the thickness (viscosity), stir in a defloculent made of equal
weights of
sodium silicate and soda ash drop by drop until the consistency is right. It
won't
take much, maybe half a teaspoon, so add it carefully, drop-by-drop, until
the
desired consistency is achieved. Record the amount of defloculent required.
Try a test cast to make sure the consistency is right, then make up your
large
batch, using the proportions you recorded when making the test batch.
This should work well. I've done this many times when making slip-cast parts
to be
added to hand-built or wheel-thrown objects.
Good luck, and don't hesitate to ask if anything is unclear.
Roger
Mercy Langford wrote:
> hi- does any body know if it's possible to make porcelain slip out of
> porcelain clay??? I have 25lbs of clay aand a blender and I need to
slipcast
> a couple of molds. How much water? any extra chemicals that I would need?
> thanks alot in advance-Mercy
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
--
Roger Korn
McKay Creek Ceramics
In AZ: PO Box 463
4215 Culpepper Ranch Rd
Rimrock, AZ 86335
928-567-5699 <-
In OR: PO Box 436
31330 NW Pacific Ave.
North Plains, OR 97133
503-647-5464
Working Potter on sun 21 apr 02
Have you considered using it to make the forms function as press molds
rather
than go the slip route?
Ceramic Design Group on sun 21 apr 02
Roger Korn has some useful and relevant points about slip making from a
plastic porcelain body.
I'll add some general things.
While it is possible to make a slip casting body from a plastic clay body,
the best ratio for casting bodies are 50 parts of non-plastic materials to
50 parts of plastic materials. This proportion will provide a high ratio of
solids relative to the amount of water needed to deffloculate it. It is
important to keep the water content as low as possible and this is why
deffloculants are used.
It is possible to use other ratios but the casting properties are severely
compromised.
Sodium silicate and soda ash are very powerful deffloculants and have a very
narrow working range and it is very easy to overuse them and render your
slip thixoid. My suggestion is to use Darvan 811 as it is makes more stable
slips with a wider working range.
The best range for specific gravities is 1.75 to 1.80 but note that each
slip has its own unique and best SG. Each slip will also have its own and
unique viscosity .
We have recently been using a #2 Zahn cup to monitor viscosity and a
Pyknometer for very accurate SG readings.
Good luck
Jonathan
Jonathan Kaplan, president
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
voice and fax 970 879-9139
info@ceramicdesigngroup.net
Plant Location:
1280 13th Street Unit 13
Steamboat Springs CO 80487
(please use this address for all deliveries via UPS, comman carrier, Fed Ex,
etc.)
"Custom design and manufacturing for the ceramic arts, giftware and pottery
industries. Molds, models, and tooling for slip casting, jiggering and
hydraulic pressing. Consultation on clay and glaze formulation, production
systems,firing, and kilns.
Ceramic Design Group on mon 22 apr 02
on
>> and a
>> Pyknometer for very accurate SG readings.
>
> Wish I had one. A glaze hydrometer gets stuck at that high an SG, and
weighing
> a
> known volumn is tedious.
>
>>
>
Hydrometers DO NOT work for determining the SG of casting slips. You can get
50 different readings on 50 different times.
Posted this before to determine the SG(glaze, casting slip whatever)
1. Obtain a container with a narrow mouth
2 Weigh the container.
3. Fill the container with water. Weigh it.
4. Subtract the weight of the container. This is the weight of the volume of
water for that container.
5. Fill the container with slip.
6. Weight it and then subtract the weight of the container. That is the
weight of the slip.
7. Divide the weight of the slip by the weight of the water.
The result is the SG of the casting slip.
Jonathan
--
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
infor@ceramicdesigngroup.net www.ceramicdesigngroup.net
(use PO BOX for all USPS correspondence)
970 879-9139
Plant Location
1280 13th Street
Steamboat Springs CO 80487
(use PLANT LOCATION for all UPS, Common Carrier, and Courier deliveries)
Mercy Langford on mon 22 apr 02
hi-since i'm in the process of figuring out this porcelain mystery -look
what
i just read in a potter's book. for a simple homemade hydrometer get a
couple
of straws(mc'donald type) and buy welding rod 1/2 in diameter and i inch
long
and glue to straw. now when you throw the straw in a good batch mark the
straw and now you know what you want from the other batches. they say it
works in glazes too. so i went to home depot but you had to buy 15.00 worth
of rodd so i went to the screws section and bought 5 that fitted my straw
and
glued it with liwuid nails. i'll be testing that theory today and i'll post
the results. just thought someone might want to know.mercy
Longtin, Jeff on mon 22 apr 02
Roger/Jonathan,
My local pottery supply shop carries the long glaze hydrometer while my
local ceramics shop carries a much shorter slip hydrometer, about 6 inches
long, with a smaller testing range. Although testing specific gravity is
something of a pain this smaller model makes it much easier.
Jeff Longtin
-----Original Message-----
From: Ceramic Design Group [mailto:info@CERAMICDESIGNGROUP.NET]
Sent: Monday, April 22, 2002 8:34 AM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: how to make porcelain slip out of clay?
on
>> and a
>> Pyknometer for very accurate SG readings.
>
> Wish I had one. A glaze hydrometer gets stuck at that high an SG, and
weighing
> a
> known volumn is tedious.
>
>>
>
Hydrometers DO NOT work for determining the SG of casting slips. You can get
50 different readings on 50 different times.
Posted this before to determine the SG(glaze, casting slip whatever)
1. Obtain a container with a narrow mouth
2 Weigh the container.
3. Fill the container with water. Weigh it.
4. Subtract the weight of the container. This is the weight of the volume of
water for that container.
5. Fill the container with slip.
6. Weight it and then subtract the weight of the container. That is the
weight of the slip.
7. Divide the weight of the slip by the weight of the water.
The result is the SG of the casting slip.
Jonathan
--
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
infor@ceramicdesigngroup.net www.ceramicdesigngroup.net
(use PO BOX for all USPS correspondence)
970 879-9139
Plant Location
1280 13th Street
Steamboat Springs CO 80487
(use PLANT LOCATION for all UPS, Common Carrier, and Courier deliveries)
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
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