Jonathan Kaplan on mon 10 nov 97
To add to this discussion and to make some corrections:
Hydrometers are exceedingly inaccurate to measure specific gravity. In
fact, no one I know even uses them any more. They will provide poor
readings, if any, at all, for slips, glazes, ect...read suspensions.
Potters work with suspensions not with solutions in most cases.
Specific gravity is the weight of a liquid relative to the same amount of
water. And in most cases, in fact in all cases, it is a pint of water. "A
pint weighs a pound, the world round, at STP (Standard Temperature and
pressure) The specific gravity of water is 1.00. Slips, glazes, all
suspended solutions(lets take glazes and slips)contain water and dry
materials. When properly mixed, flocculated or deflocculated, they will
weigh more than water.
Weigh a pint of water. It weights 454 grams. Take the same amount of glaze,
weigh it. It will be in the neighborhood of 790 to 820 grams, Divide that
number by the weight of a pint of water, 454 grams. The specific gravity
can be between 1.4-1.6, or what ever you need.
In our plant, we check the specific gravity daily, in fact at times during
glazing whether the glazes are in buckets or in the glaze fountain. After
mixing the glaze, we weigh a pint of it and note the gram weight, divide it
by 454, and note the specific gravity. Our glazes run between 1.45 and 1.60
depending on the glaze itself, the clay it needs to sit on, and the
application process.
We measure our casting slips ina similar manner.
Please, trust me on this on, don't use hydrometers for measuring specific
gravity. They don't work.
Jonathan
Jonathan Kaplan http://www.craftweb.com/org/jkaplan/cdg.shtml
http://www.ceramicsoftware.com/education/clay/kaplan1.htm
jonathan@csn.net
Ceramic Design Group Ltd./Production Services Voice:
970-879-9139 POB 775112
FAXmodem: same
Steamboat Springs, Colorado 80477, USA CALL before faxing
Plant Location: 30800 Moffat Avenue #13 Steamboat Springs Co 80487
(please use this address for all UPS, courier, and common carrier
shipments)
Judith Enright on tue 11 nov 97
Jonathan: What's a 'glaze fountain?'
-- Judith Enright
______________________________ Reply Separator _________________________________
Subject: Hydrometers and Specific Gravity
Author: Jonathan Kaplan at Internet
Date: 11/10/97 9:03 AM
----------------------------Original message----------------------------
To add to this discussion and to make some corrections:
Hydrometers are exceedingly inaccurate to measure specific gravity. In
fact, no one I know even uses them any more. They will provide poor
readings, if any, at all, for slips, glazes, ect...read suspensions.
Potters work with suspensions not with solutions in most cases.
Specific gravity is the weight of a liquid relative to the same amount of
water. And in most cases, in fact in all cases, it is a pint of water. "A
pint weighs a pound, the world round, at STP (Standard Temperature and
pressure) The specific gravity of water is 1.00. Slips, glazes, all
suspended solutions(lets take glazes and slips)contain water and dry
materials. When properly mixed, flocculated or deflocculated, they will
weigh more than water.
Weigh a pint of water. It weights 454 grams. Take the same amount of glaze,
weigh it. It will be in the neighborhood of 790 to 820 grams, Divide that
number by the weight of a pint of water, 454 grams. The specific gravity
can be between 1.4-1.6, or what ever you need.
In our plant, we check the specific gravity daily, in fact at times during
glazing whether the glazes are in buckets or in the glaze fountain. After
mixing the glaze, we weigh a pint of it and note the gram weight, divide it
by 454, and note the specific gravity. Our glazes run between 1.45 and 1.60
depending on the glaze itself, the clay it needs to sit on, and the
application process.
We measure our casting slips ina similar manner.
Please, trust me on this on, don't use hydrometers for measuring specific
gravity. They don't work.
Jonathan
Jonathan Kaplan http://www.craftweb.com/org/jkaplan/cdg.shtml
http://www.ceramicsoftware.com/education/clay/kaplan1.htm
jonathan@csn.net
Ceramic Design Group Ltd./Production Services Voice:
970-879-9139 POB 775112
FAXmodem: same
Steamboat Springs, Colorado 80477, USA CALL before faxing
Plant Location: 30800 Moffat Avenue #13 Steamboat Springs Co 80487
(please use this address for all UPS, courier, and common carrier
shipments)
M Richens on thu 13 nov 97
Hi,
If I may comment
In article , Jonathan Kaplan
writes
>----------------------------Original message----------------------------
>To add to this discussion and to make some corrections:
>
>Hydrometers are exceedingly inaccurate to measure specific gravity. In
>fact, no one I know even uses them any more. They will provide poor
>readings, if any, at all, for slips, glazes, ect...read suspensions.
>Potters work with suspensions not with solutions in most cases.
>
>Specific gravity is the weight of a liquid relative to the same amount of
>water. And in most cases, in fact in all cases, it is a pint of water. "A
>pint weighs a pound, the world round, at STP (Standard Temperature and
>pressure)
Pardon Me but..
[ Clears throat ostentatiously Hem Hem. %^) ]
In the US a pint weighs a pound _BUT_ in the UK and Australia and
similar
'A pint of water weighs a pound and a quarter'
This is because the US has 16 fluid ounces to the pint and the UK has 20
Strange innit?
>The specific gravity of water is 1.00. Slips, glazes, all
This is metric as gram per ml (cc) or in your case pounds per pint.
>suspended solutions(lets take glazes and slips)contain water and dry
>materials. When properly mixed, flocculated or deflocculated, they will
>weigh more than water.
>
>Weigh a pint of water. It weights 454 grams. Take the same amount of glaze,
>weigh it. It will be in the neighborhood of 790 to 820 grams,
While I agree in princple it is much better to keep units uniform.
It is probably easier to get a plastic measuring cylinder that will hold
100 gm of water (or 500 or a litre) right to the top (home brew shop).
Cut one down to size if need be or cut a 1.5 litre PET soft drink bottle
which you have marked to a litre.
As long as you have the right volume. 1000 ml of water weighs 1000 gram
(500 - 500) so you have an easy divisor as long as you know the weight
of the container then you divide the weight of the liquid, filled to the
top, by the volume. The larger the volume you use the lower the error as
long as your scales cope.
Max
--
Max Richens max@richens.demon.co.uk +44 (0) 1925756241
Enamel Consultant - Ceramist - Analyst programmer
Software for Batch Formulation and Millroom control.
ZALT@aol.com on thu 13 nov 97
In a message dated 97-11-10 09:35:09 EST, you write:
<< d o >>
Jonathan;
Your advice on the spacific gravity is well said. As for my self, I weigh
200 cc of glaze divide by two and move the decimal over to the left by two.
It is much easier on the brain. I would guess that you could use a litre
measure and divide by 10 move the decimal two to the left to get the same
figure. Using the litre would give a more precise figure. Of course with
hand held calculators, dividing by 454 should present little problem. That
is providing one has it handy when doing the SG check.
What is the impact of solubles in the glaze in regards to the SG?
What is the use of the viscosity meter and is it a good idea to use this in
addition to determining the SG?
Terrance
St Hubert, Quebec, Canada
Bill Amsterlaw on sat 15 nov 97
Hi Clayart:
Why the fuss over units of measurement? RELATIVE DENSITY (also known as
"specific gravity") is a ratio. When you divide the density of glaze by
the density of water, the units cancel out. There are no standard units in
a ratio. You could express the two densities in any units you wish and as
long as you use the same units in both numerator and denominator the ratio
will be the same.
Here is an easy way to determine relative density. All you need is a scale
and a container. It is not necessary to measure the volume in standard
units:
1. Use any container and mark with a fill-line
2. Weigh the container
3. Fill to the mark with water and weigh the water
(subtract wt of container)
4. Fill to the mark with glaze and weigh the glaze
(subtract wt of container)
5. Calculate relative density:
Divide the weight of glaze by weight of water
There is no need to measure the volume in standard units provided you weigh
both water and glaze and they are both the same volume. Here is why:
Density of glaze is weight/volume
Density of water is weight/volume
When you divide the density of the glaze by the density of water the
volumes are the same; the volumes cancel out. Whatever these volumes might
be in ml or fluid ounces or gallons or whatever is irrelevant.
- Bill Amsterlaw (wamster@slic.com)
Plattsburgh, NY
Others wrote:
>>Specific gravity is the weight of a liquid relative to the same amount of
water. And in most cases, in fact in all cases, it is a pint of water. "A
pint weighs a pound, the world round<<
>>In the US a pint weighs a pound _BUT_ in the UK and Australia and similar
'A pint of water weighs a pound and a quarter' <<
>>Weigh a pint of water. It weights 454 grams. Take the same amount of
glaze, weigh it. It will be in the neighborhood of 790 to 820 grams<<
>> While I agree in principle it is much better to keep units uniform.<<
Robert Compton on sat 15 nov 97
ZALT@aol.com wrote:
> clip--
> Your advice on the spacific gravity is well said. I weigh
> when doing the SG check.
>
> What is the use of the viscosity meter and is it a good idea to use this in
> addition to determining the SG?
>
> Terrance
reply--
I second the comments on hydrometers not being an accurate method of
testing SP. In 1984, when we added slip casting as secondary process in our
studio, I learned from experience about all the crazy results you can get from
hydrometers, weighting is the way to go for SG .And as Jeff Lawrence
commented, using a narrow necked container gives a better reading and creating
your own chart eliminates doing math each time you test for SP.
A viscosity meter, or flow meter, is indespensible in slip casting where
the flow is determinined by the amount of defocculant as well as the ratio of
water to solids (SG). A combination of proper SG and an established (your own
numbers ) rate of flow creates a slip that performs with constant results.
In glazes you generaly have suspended materials in a non defocculated
state (with notable exceptions such as ash glazes which are also soluable) and
is generally all you need to have to reproduce results in glaze application.
--
Robert Compton Phone: 802-453-3778
3600 Rt 116 http://homepages.together.net/~rcompton
Bristol, Vermont 05443 rcompton@together.net
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