bmshelton.uky on mon 26 oct 98
Recently I have been trying epsom salts as a means to keep my glazes from
settling out when stored for a few weeks between uses. It seems to work
wonders on some glazes and does OK on others. I'm happy generally. I have
noticed one small thing though.
On a couple of glazes, the absorption time seems to have been drastically
lengthened. For example, I glaze two identical pots in two different glazes
and one will dry in what I think to be a "normal" time and the other will
take about three times longer.
The glaze in question goes like this
Potash 'spar 20
whiting 20
ball clay 20
flint 30
cobalt 1
chrome .25
epsom salt teaspoon per gallon
I'm theorizing that the epsom salt is messing with the surface tension or
some other way hindering the absorption. Any Ideas? Has anyone else run
into this???
IF I am right in my theories (or not) epsom salts is suluable and I guess I
could let the glaze settle, pour off the water(measure it), and replace it
with fresh water(stir).
If done a couple of times, This should get rid of all the soluable
materials(theoretically) shouldn't it???
Bye for now, Ben
Louis Katz on tue 27 oct 98
Hi Ben,
Adding the Epsom salts increases the amount of liquid it takes to make the
glaze behave as a fluid. Therefor your glaze coat with the epsoms salts
probably has more water mixed in with it.
I have notticed that unless a glaze is very low in clay. and your's isn't , 1
teaspoon in five gallons is usually enough to keep it from settling. Maybe
your flint is unusually coarse.
Yes washing you glaze should work to remove the effects of the epsom salts,
but you probably only have to do it once, but use a large excess of water.
Louis
bmshelton.uky wrote:
>
>
> Bye for now, Ben
--
Louis Katz
lkatz@falcon.tamucc.edu
http://www2.tamucc.edu/lkatz/lkatz/
(512) 994-5987
Ron Roy on wed 28 oct 98
Hi Ben,
I don't believe you should add epsom salts (or any other flocculant) to a
glaze unless the glaze is settling out to a hard cake on the bottom of the
bucket. Guess you already know that. It is very useful when glazes are
deflocculated - but there are two other strategies you should try first -
replace any kaolin with ball clay - on a molecular level - so that you
still will have the same amount of alumina - you will need to lower the
silica a bit when you do this cause ball clay has less alumina and more
silica than kaolin. This means you can have more clay in the recipe - which
means you have better flotation. If that doesn't do the job then the next
step is to add 2% bentonite - bentonite works better with ball clay than
kaolin in counteracting settling. If those two steps don't work then add a
small amount (one table spoon) of dissolved epson salts (two tablespoons
dissolved in 1 cup of water) to two gallons of glaze - stir - let sit for a
couple of hours - if it is still settling then add another tablespoon -
etc.
Your problem with the following glaze is - you already have 20% ball clay -
and no material which tends to release sodium and deflocculate a glaze.
Adding the salts flocculated which then needs more water to flow properly -
the extra water is saturating the bisque so that it takes longer to dry -
and probably "sheeting" to boot.
Yes you can "wash" the glaze - add a lot of water - stir - and pour off the
excess the next day - you will probably have to do this a number of times -
more if you have added too much salts to begin with. No need to measure the
water - as the salts are removed you will need less and less water to get
the viscosity (of the raw glaze) right for your application.
By the way - your glaze (looks like a cone 10 glaze) is oversupplied with
CaO - does it happen to be a transparent matte?
>----------------------------Original message----------------------------
>Recently I have been trying epsom salts as a means to keep my glazes from
>settling out when stored for a few weeks between uses. It seems to work
>wonders on some glazes and does OK on others. I'm happy generally. I have
>noticed one small thing though.
>
>On a couple of glazes, the absorption time seems to have been drastically
>lengthened. For example, I glaze two identical pots in two different glazes
>and one will dry in what I think to be a "normal" time and the other will
>take about three times longer.
>
>The glaze in question goes like this
>
>
>Potash 'spar 20
>whiting 20
>ball clay 20
>flint 30
>
>cobalt 1
>chrome .25
>epsom salt teaspoon per gallon
>
>
>I'm theorizing that the epsom salt is messing with the surface tension or
>some other way hindering the absorption. Any Ideas? Has anyone else run
>into this???
>
>IF I am right in my theories (or not) epsom salts is suluable and I guess I
>could let the glaze settle, pour off the water(measure it), and replace it
>with fresh water(stir).
>If done a couple of times, This should get rid of all the soluable
>materials(theoretically) shouldn't it???
>
>Bye for now, Ben
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Stephen Mills on wed 28 oct 98
After a lot of trial and error I've come down firmly on the side of
between 1 & 3% Bentonite as a suspender. "Chemical" suspenders work well
in some glazes, but in my experience not in all. I have yet to find a
down side to using Bentonite.
Steve
Bath
UK
In message , bmshelton.uky writes
>----------------------------Original message----------------------------
>Recently I have been trying epsom salts as a means to keep my glazes from
>settling out when stored for a few weeks between uses. It seems to work
>wonders on some glazes and does OK on others. I'm happy generally. I have
>noticed one small thing though.
>
>On a couple of glazes, the absorption time seems to have been drastically
>lengthened. For example, I glaze two identical pots in two different glazes
>and one will dry in what I think to be a "normal" time and the other will
>take about three times longer.
>
>The glaze in question goes like this
>
>
>Potash 'spar 20
>whiting 20
>ball clay 20
>flint 30
>
>cobalt 1
>chrome .25
>epsom salt teaspoon per gallon
>
>
>I'm theorizing that the epsom salt is messing with the surface tension or
>some other way hindering the absorption. Any Ideas? Has anyone else run
>into this???
>
>IF I am right in my theories (or not) epsom salts is suluable and I guess I
>could let the glaze settle, pour off the water(measure it), and replace it
>with fresh water(stir).
>If done a couple of times, This should get rid of all the soluable
>materials(theoretically) shouldn't it???
>
>Bye for now, Ben
>
--
Steve Mills
Bath
UK
home e-mail: stevemills@mudslinger.demon.co.uk
work e-mail: stevemills@bathpotters.demon.co.uk
own website: http://www.mudslinger.demon.co.uk
BPS website: http://www.bathpotters.demon.co.uk
Craig Martell on wed 28 oct 98
Hi:
I've used epsom salts to suspend glazes too. The way I was taught to use
this stuff was: Make a saturated solution by adding the salts to water
about a pint or so) until no more will dissolve. Then using an eye
dropper, add a couple of drops at a time to your glaze until you get the
desired "set". If you add to much epsom solution and the glaze is too
thick, don't just add water to thin it. You have to add fresh glaze with no
epsom salts until you even things out. If you just add water, you will have
a suspension that seems to apply the correct amount of glaze but will
actually be too thin.
The lengthy drying of the glaze receipe that you sent was probably due to
the high ball clay content. That glaze probably doesn't need epsom salts
because a glaze with 20% ball clay should not have suspension problems.
I've noticed that glazes I use with high clay content, say around 15% and
more, will take longer to lose the water than glazes with less clay. If I
use epsom salts to "set" these glazes or add suspenders such as bentonite or
macaloid, or vee gum "t", they will take even longer. If you put a high
clay glaze with a long drying time on a thin piece and glaze both sides at
once, the chances of the glaze "shelling" and popping off when dry are
pretty good.
regards, Craig Martell-Oregon
Donn Buchfinck on thu 29 oct 98
if your glaze settles out then goto your hardware store and buy a small bottle
of muriatic acid
mix the glaze up and add 1 tablespoon to 10 thousand gram batch of glaze.
it will thicken up the glaze and you will have to add some more water but it
works like a charm.
just remember that when you suspend a glaze like this the application changes,
and it will take a little longer for the water to be absorbed into the pot.
Donn Buchfinck
Phyllis E. Tilton on sat 31 oct 98
Hi Donn: I read this same message the other day and have been surprised that
no one replied since potters are pretty safety minded. Did the bottle of acid
have the cautions about handling, breathing fumes, storage? Was it in plastic
or glass? It can be caustic and burn. I know it is used in swimming pool
maintenance and has many uses in the building trades. Please exercise care-
wear rubber gloves in handling, wash the measuring utensils, and store
carefully.
It brought the question to my mind as to why it worked as a suspending agent.
Does it alter the pH? Is there a chemical reaction with something in the
glaze?
It is interesting to me about the restrictions put on pharmacies. In some
states, they have to keep poison registers and have people sign for poisonous
purchases. I don't think that the same things apply to hardware stores,
agricultural supply houses, etc.
The pharmacies are periodically inspected and various 'registers' are checked.
Phyllis Tilton
Tom Buck on mon 2 nov 98
Phyllis Tilton:
HCl hydrochloric acid (muriatic) yields H+ ions which alter the
charge on clay particles so that they do not agglomerate and hence settle
into a pancake. MgSO4 (epsom salts) yields Mg++ ions which will have a
similar effect. So if hardpan is a problem, add the acid or the salt. And
yes, HCl must be handled with due care (burns the skin) but it is not as
dangerous as some other chemicals potters routinely handle.
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
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