Nancy Udell on sat 7 jul 07
Decided to try a hydrometer in this current round of glaze mixing.
Which one to get? Where to start. A quick search in the archives
came up with (as always) a lively discussion of the subject and (as
usual) an incredibly detialed and helpful message from Vince in 1998
-- even including a URL and model # -- both still good. THANK YOU
clay art and Vince.
Vince Pitelka on tue 8 sep 98
Six months ago or so I posted a message about a hydrometer I
found in the
VWR Scientific Products catalog (800/932-5000 - www.vwrsp.com),
which
according to the description seemed especially appropriate for
use with
terra sig (and thin slips and glazes). I have not ordered this
hydrometer,
but all the specs are right. It is designed for testing small
volumes of
heavy liquids, is 6.5" (165mm) long, has a s.g. scale from 1.00
to 2.00, and
costs $19.97 each - catalog number is #34640-207.
John Rodgers on sat 7 jul 07
Nancy,
I know there are many who think hydrometers are wonderful, but if you
have a decent scale, you don't even need a hydrometer. Unless you need
speed in measuring, a hydrometer is a waste of money. Weigh out equal
volumes of water and glaze, divide the weight of the water into the
weight of the glaze, and Voila!! you have the specific gravity or
density of the glaze. Add or remove water to adjust the density.
Establishing the density of your glaze for your specific operation is
the key to good glazing and good glazes after firing.
Regards,
John Rodgers
Chelsea, AL
Nancy Udell wrote:
> Decided to try a hydrometer in this current round of glaze mixing.
> Which one to get? Where to start. A quick search in the archives
> came up with (as always) a lively discussion of the subject and (as
> usual) an incredibly detialed and helpful message from Vince in 1998
> -- even including a URL and model # -- both still good. THANK YOU
> clay art and Vince.
>
> Vince Pitelka on tue 8 sep 98
>
> Six months ago or so I posted a message about a hydrometer I
> found in the
> VWR Scientific Products catalog (800/932-5000 - www.vwrsp.com),
> which
> according to the description seemed especially appropriate for
> use with
> terra sig (and thin slips and glazes). I have not ordered this
> hydrometer,
> but all the specs are right. It is designed for testing small
> volumes of
> heavy liquids, is 6.5" (165mm) long, has a s.g. scale from 1.00
> to 2.00, and
> costs $19.97 each - catalog number is #34640-207.
>
> ______________________________________________________________________________
>
> 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.
>
>
Tom at Hutchtel.net on sun 8 jul 07
Actually it gets easier than this. Once you get the glaze to the
consistency you want to work with ( it differs for different people and
methods), you just need to have a consistent container. We use a small 8-oz
plastic jar. Fill it so the glaze just fills the ring under where the cap
goes (filling exactly every time is the only tricky part), weigh it, record
that weight, and then every time you use the glaze, make sure the glaze is
that weight. Guarantees that the solids to water ratio is the same every
time.
If it's a bit light, let it settle and take off some water, if it's a bit
heavy (the more frequent case), add a little water.
As explained many times before on the list, the reason that a hydrometer is
inaccurate is that they are made for solutions. Glazes are suspensions. In
a suspension, the particles cause drag on the sides of the hydrometer. The
thicker the glaze, the greater the drag. Try this test if you have access
to a hydrometer. Stir up your glaze. Put in the hydrometer very carefully.
Or use Mel's famous stick with a weight. Let it settle, and record the
reading. Now gently push it further down, let it settle and record. I will
guarantee it will be different. If you are looking for glazing consistency,
you cannot use a hydrometer, you must weigh.
Tom Wirt
Hutchinson, MN
twirt@hutchtel.net
www.claycoyote.com
----- Original Message -----
From: "John Rodgers"
Subject: Re: Hydrometers, Clayart & Vince
> I know there are many who think hydrometers are wonderful, but if you
> have a decent scale, you don't even need a hydrometer. Weigh out equal
> volumes of water and glaze, divide the weight of the water into the
> weight of the glaze, and Voila!! you have the specific gravity or
> density of the glaze. Add or remove water to adjust the density.
> Establishing the density of your glaze for your specific operation is
> the key to good glazing and good glazes after firing.
>
Michael Wendt on mon 9 jul 07
Despite claims to the contrary, hydrometers
work fine in glazes. I have used both methods
and compared results. They match.
Some rules apply:
1) your glaze must be deep enough to allow
the hydrometer to float and not hit bottom.
2) the glaze must be freshly stirred.
3) the hydrometer must be WET first
4) lower the hydrometer slowly to avoid
having it sink too far (there's a reason)
5) as soon as you are near the expected
reading you may let go.
6) tap the side of the container gently
until the hydrometer stops sinking.
7) record the reading.
8) add water if needed, a little at a time.
The reason you must not overshoot
is the glaze then obscures the markings.
Gentle tapping overcomes the slight
ability of solid -liquid suspensions to
exert shear and drag forces on the
hydrometer.
Unlike the container method, I can adjust
the SG of a glaze in a few seconds and
merely rinse the hydrometer and return
it to the shelf.
If you don't already have a hydrometer
but do have a scale, save the money and
use Tom's method. (see below) You'll like it fine.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, ID 83501
USA
208-746-3724
http://www.wendtpottery.com
wendtpot@lewiston.com
Tom Wirt wrote:
Actually it gets easier than this. Once you get the
glaze to the
consistency you want to work with ( it differs for
different people and
methods), you just need to have a consistent container.
We use a small 8-oz
plastic jar. Fill it so the glaze just fills the ring
under where the cap
goes (filling exactly every time is the only tricky
part), weigh it, record
that weight, and then every time you use the glaze,
make sure the glaze is
that weight. Guarantees that the solids to water ratio
is the same every
time.
If it's a bit light, let it settle and take off some
water, if it's a bit
heavy (the more frequent case), add a little water.
John Sankey on mon 9 jul 07
I don't recommend a hydrometer, it measures only a secondary
characteristic of a glaze. Instead, measure the thickness of the
glaze layer deposited by your personal dipping method and bisque.
See
http://sankey.ws/pottery2.html
for the method. It measures directly what really matters.
--
(Add 'Byrd' to the subject line of your reply to get through my spam filter)
Ivor and Olive Lewis on mon 9 jul 07
Dear John Rodgers,=20
Sounds an ideal way to do it. A litre of water to a litre of glaze =
powder.
But how do you adjust your mass or volume to cope with the entrained air =
in powdered ingredients? This source of error is eliminated when you are =
using a Hydrometer on a fully slaked fluid glaze batch.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
<water into the
weight of the glaze, and Voila!! you have the specific gravity or =
density of the glaze.>>
Ben Shelton on tue 10 jul 07
I use a 100ml graduated cylinder I bought from US plastics to measure out
100 ml of well stirred glaze. If you zero your scale with the empty dry
cylinder on it then the scale will weigh just the glaze inside. I use 100ml
because it makes the math easy. If 100 ml glaze weighs 152g then the glaze
has a specific gravity of 1.52. 152 glaze weight divided by 100 water
weight (152/100=1.52)
IF you want to go with the weigh-a-sample method this makes life a little
simpler.
FWIW the cylinder was less than $10 in US money delivered.
Ben
Taylor Hendrix on wed 11 jul 07
Large syringes from the vet that can hold 100ml work just as well for
sampling your glaze. You can even double check using distilled water.
Just have a tared container on your balance and deposit 100ml from the
syringe.
Most excellent for wet blending glazes in glaze tests too. Never throw
that stuff away.
Taylor, in Rockport TX
On 7/10/07, Ben Shelton wrote:
> I use a 100ml graduated cylinder I bought from US plastics to measure out
> 100 ml of well stirred glaze.
Jennifer Boyer on wed 11 jul 07
I agree with you, Ben that a graduated cylinder is an essential tool
for this kind of measuring. Mine is very narrow, so the measurement
of 100 ml is very accurate. I'm not sure someone would get consistent
results using a wider container like a yoghurt container. The narrow
graduated cylinder is the way to go! You can get a small one since
100 ml is all you need to measure.
Jennifer
On Jul 10, 2007, at 8:01 AM, Ben Shelton wrote:
> I use a 100ml graduated cylinder I bought from US plastics to
> measure out
> 100 ml of well stirred glaze. If you zero your scale with the empty
> dry
> cylinder on it then the scale will weigh just the glaze inside. I
> use 100ml
> because it makes the math easy. If 100 ml glaze weighs 152g then
> the glaze
> has a specific gravity of 1.52. 152 glaze weight divided by 100 water
> weight (152/100=1.52)
>
>
> IF you want to go with the weigh-a-sample method this makes life a
> little
> simpler.
>
> FWIW the cylinder was less than $10 in US money delivered.
>
> Ben
>
> ______________________________________________________________________
> ________
> 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.
*****************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
*****************************
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