Victoria Cherney on sat 4 jun 05
This is a very basic questions, to which I feel embarrassed not to know
the answer. In reading glaze recipes, the amount of water is never
stated. How do I know how much water to add to the dry ingredients in
one or another glaze recipe?
Thanks in advance,
Victoria
befuddled in Vermont
Marcia Selsor on sat 4 jun 05
It really depends on the chemicals you are using...wood ash has a lot
of mass per light weight. I usually look at the dry mix, fill an
equivalent size bucket with an equal mass, add the dry to the water
and add more water as I sieve. I need to wash more through the sieve,
etc. Then, dare I say, I stick a dry finger into the mix and look at
the lines on my knuckle. I should be able to see a knuckle pattern
with the glaze covering the skin. This is the famous "dry finger
test". This works if you aren't using toxic chemicals.
Marcia Selsor
must go out and start working in the yard!
On Jun 4, 2005, at 8:44 AM, Victoria Cherney wrote:
> This is a very basic questions, to which I feel embarrassed not to
> know
> the answer. In reading glaze recipes, the amount of water is never
> stated. How do I know how much water to add to the dry ingredients in
> one or another glaze recipe?
>
> Thanks in advance,
>
> Victoria
> befuddled in Vermont
>
> ______________________________________________________________________
> ________
> 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.
>
>
Snail Scott on sat 4 jun 05
At 10:44 AM 6/4/2005 -0400, Victoria wrote:
>This is a very basic questions, to which I feel embarrassed not to know
>the answer. In reading glaze recipes, the amount of water is never
>stated. How do I know how much water to add to the dry ingredients in
>one or another glaze recipe?
This is another one of those annoying answers:
"It depends". ;)
Some glaze materials need more water than others
to produce a slurry of the proper consistency. Some
clays need a thicker slurry than others to achieve
the right glaze thickness on the surface. Some
glazes need to be applied thicker than others to
produce the desired result after firing. And one
person's desired result may not be the same as
another's. If you use a recipe that someone gave you,
you can ask them how much water they like to use in
it, but unless they are using the same clay, thrown
or handbuilt or cast to the same thickness, bisque-
fired to the same cone, and glazed by the exact same
technique, their 'right answer' may still not apply
to you. Only actual testing on YOUR work can really
answer the question.
As a VERY general rule of thumb, 10,000 grams of
dry glaze materials will make 5 gallons of glaze
when water is added. Many people aim for a slurry
which is thin enough the show the contour of the
nail-bed when you dip a fingertip in, but this is
only a starting point. Modify as needed.
If the recipe contains a lot of frit, you may need
less water, so 10,000 grams may only make 3 or 4
gallons of glaze. If the recipe has a lot of
gerstley borate in it, 10,000 grams might fill two
5-gallon buckets when adequately wetted: i.e. more
water is needed for the same weight of dry materials.
If you are brushing the glaze, it will work better
if the glaze is thicker (less water). If you are
dipping, it will require more, and if you are
spraying it, it will need to be even thinner (still
more water).
CLay which is bisqued to lower temperatures tends to
be more absorbent than the same clay bisqued to higher
temperatures, and high-fire clay is generally more
absorbent than low-fire clay at any given bisque
temperature, and bisqued clay is generally more
absorbent than unfired (dry/green) clay. So, make the
glaze with more water for absorbent clay (if you are
dip-glazing), since it will take up a thicker coating.
(If you are brushing or spraying, absorbency doesn't
determine the thickness, your application does.)
When you test a glaze, make sure to test various
thicknesses of the same glaze, using whatever method
of application you intend for your final work. It
doesn't tell you much if you dip your tests, then
brush the actual work. Glazes can vary radically
at differing thicknesses, sometimes turning out with
very different colors or textures. You might even
choose to take advantage of this in your design
process, but you need to know how thick it needs
to be for each result.
A common method of testing is to make a slab with
a similar thickness and texture to your intended
work, about 2" x 5", with a 'foot' so it will stand
up in the kiln. Bisque these slabs to your normal
bisque cone. For testing glazes, dip the test into
the glaze, holding onto the 'foot', until it's
all submerged but the bottom inch or so. Hold for
a few seconds and remove. Let it dry until all the
visible moisture has sunk in or evaporated. Then
repeat, but don't dip it as deeply, so that an
inch or two of the first dip is still exposed,
then pull it out and let it dry a bit. Then repeat,
only dipping the top portion. This creates three
different thickness tests on each test piece. The
same range can be produced with brushing, by putting
one coat on most of it, then a second on part of it,
and a third on just the top.
When doing tests of a new glaze, always leave a good
margin of unglazed clay at the bottom, and keep the
thickest parts of the test at the top. Thicker glazes
tend to drip more, so by keeping the thicker tests
at the top, it's got room to run in case it tries to
flow off onto your shelves. (If the thickest part of
the test gets deep cracks as it dries,
Some people use careful measurements when they add
water, but since evaporation (and absorption into clay
if dipping) can alter the mixture over time, it's
not actually that useful. Most people use the 'dip
a fingertip' method of checking thickness of a glaze
batch each time they use it, and add water 'to eye'
as needed. It's more accurate to measure the specific
gravity with a hydrometer, but for that to be useful,
you have to know how thick it ought to be, and only
testing will tell you that. People who do production
work and who rely on consistent results will benefit
the most from this, as will people who choose to use
very 'fussy', thickness-sensitive glazes.
For starting out, though, shoot for a slurry about as
runny as cream (if dipping), and modify as needed for
the variables I mentioned above, until YOU like the
result.
-Snail
william schran on sat 4 jun 05
Vermont Victoria wrote:> In reading glaze recipes, the amount of
water is never
stated. How do I know how much water to add to the dry ingredients in
one or another glaze recipe?<
The amount of water in any given glaze will vary according to the
materials in the glaze.
When I make tests I start with 1/4 cup water to 100 grams of dry
glaze materials.
Bill
Donald G. Goldsobel on sat 4 jun 05
A variation on the knuckle pattern is " it is thick enough when you dip in a
dry finger and you can see the outline of the cuticle of your fingernail"
It works on all the glazes I use. Make sure the finger is dry!
John Rodgers on sat 4 jun 05
Victoria,
I don't know any real way to know in advance how much water to mix with
a given batch of dry glaze mix. For me it is always a matter of trial
and error .... but educated and experienced trial and error.
I begin by having a mixing bucket plus the bucket with dry glaze and a
bucket with water. I put water in the bucket , then add dry glaze to get
it wet, but soupy - definitely not runny. I do it by sight. Then I add a
bit more water, then a bit more glaze. I keep this up but always stay of
the side of soupy - but stiff soupy. Once all the glaze is added. I
begin adding more water, and mixing thoroughly. Each time I add water, I
check the density or specific gravity of the glaze - ie - the ratio of
the weight of a given volume of glaze compared to the weight of an
equal volume of plain water. I play with my glazes until I have a
specific knowledge of the best density for best performance of the
glaze. Once I have that established, I can repeat the best performance
parameters every time. That is the way I achieve consistency in the
performance of a glaze from one batch to the next, from one load of pots
to the next, from one firing to the next.
The name of the game is to be able to control all the variables in doing
pottery. The density of the glaze is one of those variables. I glaze
most often by dipping. I control the glaze thickness by timing the
period of immersion of the pot in the glaze. If the density is not
controlled, then my timing will not produce a consistent glaze
thickness. A 15 second immersion of a pot in a glaze of density 1.0 will
produce a glaze thickness very different from a 15 second immersion of a
pot in a glaze density of 1.5. When fired that density difference shows
up in the finished piece.
Play with the glaze. Work out the numbers. Write it all down. Glaze,
density, time, type of clay. All factors that can be controlled to
produce consistent glazing and finished appearance over and over.
Regards,
John Rodgers
Chelsea, AL
Victoria Cherney wrote:
> This is a very basic questions, to which I feel embarrassed not to know
> the answer. In reading glaze recipes, the amount of water is never
> stated. How do I know how much water to add to the dry ingredients in
> one or another glaze recipe?
>
> Thanks in advance,
>
> Victoria
> befuddled in Vermont
>
> ______________________________________________________________________________
>
> 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.
>
>
Marcia Selsor on sun 5 jun 05
Victoria,
Snail brought up some very important points such as application, frit
percentage. There are many variables to consider.
> Another though would be to add a tablespoon of epson salts to a 5
> gallon bucket of glaze that has a lot of frit. This will help keep
> it suspended and not settle too fast.
Marcia Selsor
> ______________________________________________________________________
> ________
> 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.
>
>
Eleanora Eden on mon 6 jun 05
Victoria,
A couple of ideas I haven't seen covered in this thread:
I use a viscosometer rather than a hydrometer to get consistent
results with glaze and also with slip. This is a little cup with a
little hole in the bottom and you scoop up your liquid and time how
long it takes to completely drain out. I once got a person at Duncan
to tell me that for dipping their glaze it should be between 18-25
seconds and that definitely seems to be the ball-park for the stuff I
use.
When you have your slip or glaze just perfect you do this test and
record the time.
When I don't know how much water to add to a new clay or glaze recipe
I weigh out more than I think I will need and then weigh the
container again after I got it just right, so then I know the weight
of exactly how much water I used. I do this with a small batch not a
big batch. Then you have the amount you'll need for the big batch
without guessing.
Eleanora.....also befuddled in Vermont but not on this particular point......
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