John Rodgers on thu 18 may 06
Beth,
You want density of glaze, and viscosity of the glaze.
Density (Specific Gravity) - I use an Ohaus gram scale, and I zero the
scale with a clear plastic 1 quart paint container on the scale. I then
fill it with water to the one pint line and weight the water. Then I do
the same with the glaze. I devide the weight of the water into the
weight of the glaze. The number derived will be the density If you do
the whole thing in metri, it comes out with a decimal number like 1.2 or
1.5 etc. This number represents the desity in grams per milliliter. As a
matter of practicality, only the number matters, not the units of
measure. That 1.2 means the glaze is 1.2 times greater in weight that an
equal volume of water. Many of my glazes work best at 1.5 If I have had
a water loss, I may need to dilute the glaze with more water to arrive
at that number. When glazing on a very dry day, your glaze density could
increase upward, and you could get 1.7, 1.9, etc, If best performance is
at 1.5, then of course you must add water to dilute it back down to 1.5.
If the number is low, let the glaze sit 24 hours and then drain some
water off the top and re-adjust. Knowing the best performance number for
your glaze is very important for precise control.
The viscosity is simply the flow rate of a specific volume of the glaze.
It is done with a specific volume of glaze through a specified orifice
in a specified time. Coyote Clay in Albuquerque has a slick little
plastic device that make this viscosity test extremely easy. Cost is
$4.95. Well worth it. Just dip into the glaze and watch the clock.
Glazing is a different matter, but when slip casting it is a lifesaver.
Good luck,
John Rodgers
Chelsea, Al
Beth Eisenberg-Schapera wrote:
> Dear Clay Masters,
>
> I recently read someone's post to Neil regarding glaze viscosity (sorry, I
> forgot who wrote the post) and I wished to follow up with my own questions.
>
> I live in a VERY dry climate. At the warmest part of the day, the
> humidity can be as low as 5%! This poses enormous difficulties keeping
> glazes at the correct viscosity as I glaze from day to day. My experiences
> using a hydrometer have been mostly fruitless. Small variations in glaze
> thickness seem to make an enormous diffrence with some glazes. I think it
> would be extremely useful to be able to "weigh" the glaze to determine the
> correct viscosity with each use and add water accordingly. Do lots of
> other people do this? How is this technique done?
>
> Could others provide additional suggestions on getting the
> right "thickness" for glazes.
>
> Additionally, what materials can I add to commercially prepared glazes to
> enhance brushability? Can I use the same additives to my own glazes
> recipes?
>
> Thanks to all those who responded about wax and latex. I have bought
> several new waxes and am experimenting with all. I had no idea that so
> much variation existed between different brands. I also loved the latex
> resist but I found, as several suggested, that a flakey edge was
> created. I haven't figured out how to smooth the flakey edge easily so I
> welcome suggestions about this too.
>
> Best Regards,
> Beth Eisenberg-Schapera
> Bishop, CA
> (5 hours from a shopping mall but living in the most beautiful place in
> the world)
> PS. Can someone explain how I post a link on Clayart? Technically
> challenged, plse keep explanation simple ;)
>
> ______________________________________________________________________________
> 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.
>
>
>
Beth Eisenberg-Schapera on thu 18 may 06
Dear Clay Masters,
I recently read someone's post to Neil regarding glaze viscosity (sorry, I
forgot who wrote the post) and I wished to follow up with my own questions.
I live in a VERY dry climate. At the warmest part of the day, the
humidity can be as low as 5%! This poses enormous difficulties keeping
glazes at the correct viscosity as I glaze from day to day. My experiences
using a hydrometer have been mostly fruitless. Small variations in glaze
thickness seem to make an enormous diffrence with some glazes. I think it
would be extremely useful to be able to "weigh" the glaze to determine the
correct viscosity with each use and add water accordingly. Do lots of
other people do this? How is this technique done?
Could others provide additional suggestions on getting the
right "thickness" for glazes.
Additionally, what materials can I add to commercially prepared glazes to
enhance brushability? Can I use the same additives to my own glazes
recipes?
Thanks to all those who responded about wax and latex. I have bought
several new waxes and am experimenting with all. I had no idea that so
much variation existed between different brands. I also loved the latex
resist but I found, as several suggested, that a flakey edge was
created. I haven't figured out how to smooth the flakey edge easily so I
welcome suggestions about this too.
Best Regards,
Beth Eisenberg-Schapera
Bishop, CA
(5 hours from a shopping mall but living in the most beautiful place in
the world)
PS. Can someone explain how I post a link on Clayart? Technically
challenged, plse keep explanation simple ;)
Ellen Currans on thu 18 may 06
In a message dated 5/18/06 2:15:36 PM !!!First Boot!!!,
caterbeth@EARTHLINK.NET writes:
> I think it
> would be extremely useful to be able to "weigh" the glaze to determine the
> correct viscosity with each use and add water accordingly. Do lots of
> other people do this? How is this technique done?
>
> I didn't find a hydrometer very useful either. I do weigh my glazes to
> assure the same viscosity every time I glaze. Here is how I do it. I have a
> small plastic bottle (any bottle that will hold 1 or 2 cups of glaze will do)
> that came from a hair dye kit and holds about 1 1/2 cups. > use the same
> bottle every time. When I think the glaze I am using is correct for my work, I
> weigh a full bottle of glaze on the gram scale. In my case, I put on the 600
> gram weight and use no pan. Whatever the full bottle weighs ( 642 or 666,
> etc.) is what I use for the viscosity of that particular glaze. Over the years
> I have gradually found that thinner is better for my work and have changed
> the target number. The number has no relation to the actual weight of the
> materials or the molecular formula or anything like that. It is just a number
> that tells me when I've got it right for me. If you use a smaller bottle you
> may not need the 600 grm weight and your number will be lower. Almost every
> glaze is slightly different. It may take time to find what is best for each
> glaze, but it eventually takes a lot of the guess work out of glazing.
>
> If you want to have a viscosity figure that would translate to another
> potter's work, you would need to use a 100 ml graduated cylinder (if that is the
> correct term) and do a little math. I prefer not to have to deal with that
> very fragile, tippy cylinder when I am in the midst of glazing frenzy. My
> little plastic bottle washes out quickly, drains upside down, and doesn't get
> hurt it it falls into the sink.
>
> Ellen Currans
>
Bruce Girrell on thu 18 may 06
Glaze weight/density and viscosity are very different properties. For
example, the viscosity can be changed dramatically by the addition of a
small amount of CMC gum which would change the density very little.
All you need to know about the viscosity is how to make it repeatable, you
don't really need to know the actual viscosity (in centipoise). To do that
all you need is a very simple device.
1) Get a small plastic cup. A half cup or one cup measuring cup would be OK,
but the more conical in shape, the better.
2) Drill a small hole, about 1/8" in diameter, in the center of the bottom
of the cup.
3) Get a timing device with a sweep second hand.
4) Get a glaze that is working well for you and dip the cup into the glaze,
filling it completely.
5) Cover the hole in the bottom and withdraw the cup from the glaze. Let the
excess glaze drip off of the cup or wipe most of it off (but don't spill the
contents of the cup).
6) Uncover the hole in the bottom of the cup when the second hand of your
timer passes a convenient marker and allow the glaze to drain back into the
bucket.
7) Continue timing until the glaze stops flowing in a constant stream and
begins to drip. Record the time.
8) Repeat the test at least three times to ensure that you get a consistent
result because this will be the reference time for future tests.
The time that you obtain from your tests can now be used to test other
glazes. Dip the cup in the test glaze and time it as before. If the time is
shorter than the reference time then the viscosity of your test glaze is too
low (it's too "thin"). If the time is longer than the reference time then
the viscosity of your test glaze is too high (it's too "thick"). Adjust as
necessary to make the time of your test glaze match that of the reference
glaze.
Bruce "Mr. Viscosimeter" Girrell
Barbara Lewis on thu 18 may 06
Ellen: Thanks for sharing this information. As I was reading your post, a
thought came to me that after you're satisfied with the viscosity of the
glaze, you could keep the glaze in the hair color bottle for touch-ups
during the glazing process. And, then empty the bottle when you're finished
glazing. It would require you to have more than one bottle, but at the rate
I'm graying, that shouldn't be a problem. :>) Barbara
----- Original Message -----
From: "Ellen Currans"
To:
Sent: Thursday, May 18, 2006 11:48 AM
Subject: Re: Glaze weight and viscosity
> In a message dated 5/18/06 2:15:36 PM !!!First Boot!!!,
> caterbeth@EARTHLINK.NET writes:
>
>
>> I think it
>> would be extremely useful to be able to "weigh" the glaze to determine
>> the
>> correct viscosity with each use and add water accordingly. Do lots of
>> other people do this? How is this technique done?
>>
>> I didn't find a hydrometer very useful either. I do weigh my glazes to
>> assure the same viscosity every time I glaze. Here is how I do it. I
>> have a
>> small plastic bottle (any bottle that will hold 1 or 2 cups of glaze will
>> do)
>> that came from a hair dye kit and holds about 1 1/2 cups. > use the same
>> bottle every time. When I think the glaze I am using is correct for my
>> work, I
>> weigh a full bottle of glaze on the gram scale. In my case, I put on the
>> 600
>> gram weight and use no pan. Whatever the full bottle weighs ( 642 or
>> 666,
>> etc.) is what I use for the viscosity of that particular glaze. Over the
>> years
>> I have gradually found that thinner is better for my work and have
>> changed
>> the target number. The number has no relation to the actual weight of
>> the
>> materials or the molecular formula or anything like that. It is just a
>> number
>> that tells me when I've got it right for me. If you use a smaller
>> bottle you
>> may not need the 600 grm weight and your number will be lower. Almost
>> every
>> glaze is slightly different. It may take time to find what is best for
>> each
>> glaze, but it eventually takes a lot of the guess work out of glazing.
>>
>> If you want to have a viscosity figure that would translate to another
>> potter's work, you would need to use a 100 ml graduated cylinder (if that
>> is the
>> correct term) and do a little math. I prefer not to have to deal with
>> that
>> very fragile, tippy cylinder when I am in the midst of glazing frenzy.
>> My
>> little plastic bottle washes out quickly, drains upside down, and doesn't
>> get
>> hurt it it falls into the sink.
>>
>> Ellen Currans
>>
>
> ______________________________________________________________________________
> 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.
>
John Rodgers on fri 19 may 06
Oops!!
Not Coyote Clay with the slick little thingy, but New Mexico Clay with
the slick little thingy, for doing a viscosity check - cost $4.95
It's actually a paint thinning device - something to check your paint
flow if you are a painter, as in house painter. They have calibrated it
for slip at 23 seconds. Glaze works in it too.
John Rodgers
Chelsea, AL
| |
|
