Carolynn Palmer on thu 21 oct 99
When I read Jeff Zamek's article about correcting glazes in the Sep 99 CM, I
purchased liquid CMC from Great Lakes Clay Company and added it to my problem
glaze. (I had read on Clayart that CMC was difficult to add to a glaze that
was already mixed, so I opted for the premixed liquid.)
This CMC immediately caused the glaze to settle like cement. The glaze is
now an unbelievable solid, hard lump in the bottom of the bucket. All of my
reading about CMC had led me to believe that it would cause the glaze to stay
in suspension.
This problem glaze always crawls if there are multiple applications. It
dries to a powdery surface immediately upon dipping the pot and the CMC
seemed like a reasonable solution.
Carolynn Palmer, Somerset Center, Michigan
Tom Buck on fri 22 oct 99
CP:
Unfortunately few advisers give the full name of CMC, namely,
Carboxy Methyl Cellulose Sodium Salt, and the liquid form of CMC would be
fully ionized, ie, Na+ ions and CMC- ions. So when you added it to your
glaze slurry, boom, the Na+ ions floc'd the glaze and floc'd it hard. To
prevent this happening, always add Epsom salts to the galze water -- 10 -
15 grams per kilogram of glaze solids. Epsom Salts, or Magnesium Sulfate,
supplies Mg++ ions and SO4-- ions. The Mg++ ions do combine with the glaze
particles but they do not cause full flocculation, only a first stage that
thickens the glaze a bit, and the particles largely stay in suspension,
settle slowly to a soft mush. The Mg++ ions then effectively keep most of
the Na+ ions away from the glaze particles.
Tom Buck )
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
Tom Buck on sun 24 oct 99
RR:
Gee I hate the words floc/defloc. Generally, mix em up. I shall
prefer the word "aglomerate" instead. When Na+ ions are in the glaze
water, they will agglomerate the glaze solids, clayey stuff mostly, and
cause the particles to clump together and settle rapidly to form a hardpan
(because of attraction by electrical forces). The Epsom Salts, put in the
water before adding the solids, slows down the agglomeration of the glaze
solids and so prevents formation of hardpan. The Mg++ ion from Epsom Salts
manages to do this by competing with Na ion for chemially active sites on
the large particles of glaze material, generally getting there first, and
so modifies the attraction.
Thanks for noticing my goof. Be good. BFN. Peace. Tom.
Tom Buck )
tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
On Sat, 23 Oct 1999, Ron Roy wrote:
> Hi Tom,
>
> I think you mean the CMC defloc'd the glaze - and the Epson floc'd it - right?
>
> R
>
> >----------------------------Original message----------------------------
> >CP:
> > Unfortunately few advisers give the full name of CMC, namely,
> >Carboxy Methyl Cellulose Sodium Salt, and the liquid form of CMC would be
> >fully ionized, ie, Na+ ions and CMC- ions. So when you added it to your
> >glaze slurry, boom, the Na+ ions floc'd the glaze and floc'd it hard. To
> >prevent this happening, always add Epsom salts to the galze water -- 10 -
> >15 grams per kilogram of glaze solids. Epsom Salts, or Magnesium Sulfate,
> >supplies Mg++ ions and SO4-- ions. The Mg++ ions do combine with the glaze
> >particles but they do not cause full flocculation, only a first stage that
> >thickens the glaze a bit, and the particles largely stay in suspension,
> >settle slowly to a soft mush. The Mg++ ions then effectively keep most of
> >the Na+ ions away from the glaze particles.
> >
> >Tom Buck )
> >tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
> >mailing address: 373 East 43rd Street,
> > Hamilton ON L8T 3E1 Canada
>
> Ron Roy
> 93 Pegasus Trail
> Scarborough
> Ontario, Canada
> M1G 3N8
> Evenings 416-439-2621
> Fax 416-438-7849
>
>
Tony Hansen on sun 24 oct 99
> When I read Jeff Zamek's article about correcting glazes in the Sep 99 CM, I
> purchased liquid CMC from Great Lakes Clay Company and added it to my
> This CMC immediately caused the glaze to settle like cement. The glaze is
> now an unbelievable solid, hard lump in the bottom of the bucket. All of my
> reading about CMC had led me to believe that it would cause the glaze to
> stay in suspension.
CMC hardens an otherwise powdery glazes. It is like glue. It is not suspend.
Use Bentonite or make sure glaze has adequare kaolin or ball clay.
For information search "CMC" at http://ceramicsearch.com
Here is some info on CMC:
An organic sodium carboxymethylcellulose that acts to harden unfired
ceramic glazes (cement the particles together) for safer handling of the
ware. Highly fritted glazes (lacking clay content) used in factory settings
benefit greatly from the addition of gum. Gum additions are often
unnecessary if the glaze has natural hardening properties (i.e. from
20% or more clay). However gum is an important addition to stain
mixes that are applied over-glaze by stamping or painting.
Gum can help suspend and stabilize glaze slurries somewhat,
however other additives (an adequate amount of the right clay
in the batch) are also effective.
An important side effect of gum additions is that they cause slower
drying. While this is advantageous for brushing glazes, it can
make it very difficult to achieve an adequate glaze thickness and
prevent drip marks. Dipping glazes work best if they are both
naturally thixotropic and quick drying. Both of these properties
can be detrimentally affected by gum additions.
Many people make a CMC gel by mixing 30-40 grams of powder
per liter of water. This gel can then be used as part of the water
amount when mixing glazes. Incorporating propylene glycol also
can work well for making paintable stain mixes (i.e. 1 part thin
gel with 1 part glycol).
Veegum CER is a 50:50 mix of CMC and Veegum T.
Powdered gum can be very difficult to disperse in water thus it is
difficult to add it to an existing liquid batch. However if gum powder
is mixed with other dry ingredients before adding them to the
water it can be done (often 0.5-1.5%). A much more effective
method is to boil water, add about 25-30 grams of powdered
gum per litre and mix vigorously with a mechanical mixer. This
mixture must be added during mixing to replace part of the water.
It is difficult to set a standard proportion because the amount of
gum needed is totally dependent on the glaze's ability to harden.
A starting point for glazes that powder or smudge excessively
might be 1 part gum solution to 3 parts water. Performance of the
mix compared with the side effects can then be evaluated and the
proportion adjusted.
Organic binders need to burn away in such a fashion that the
particles of mineral and frit are drawn into contact with each
other to encourage reaction and prevent crawling.
Depending on time, temperature, pH, gum can be attacked by
microbes or molds. If this happens store in a cooler place,
make smaller batches, adjust the pH to make a less friendly
environment, or add an antiseptic (i.e. NaN3). Many brush on
glazes use CMC and can have a shelf life for this reason.
--
T o n y H a n s e n thansen@digitalfire.com
Don't fight the dragon alone http://digitalfire.com
Calculation/Database Software for Ceramic Industry
--
Michael Banks on mon 25 oct 99
Actually Tom, I believe that Na+ ions disperse clay particles in aqueous
suspension (I'm avoiding the word defloc here:) whereas the divalent
cations Mg++, Ca++ etc and acids (H+) cause clumping together. This is the
reason that sodium compounds are used to thin casting slips but conversely,
acids, epsom salts, calcium chloride etc, reverse this process.
The confusion arises with glaze slips because they often have low clay
content. Adding a soda compound such as CMC causes the few clay grains
present to disperse, sending the suspended solids to plummet to the bottom.
Adding Mg++, Ca++ or acid (H+) clumps the clay grains (platelets) into an
open, face to edge boxwork arrangement which helps suspend the other
non-clay ingredients. Acidifying a CMC containing, or soda-rich glaze will
often prevent undue settling. Otherwise adding epsom salts or calcium
chloride will help.
The worst case is severely settled and cemented glaze solids forming a solid
mass in the bottom of a glaze bucket. This a sure sign of excess soluble
sodium in the glaze water and a known remedy to breaking this up is to add
judicious amounts of hydrochloric acid.
Michael Banks,
Nelson,
New Zealand
----- Original Message -----
From: Tom Buck
To:
Sent: Monday, October 25, 1999 12:41
Subject: Re: Glaze Crawling and CMC
> ----------------------------Original message----------------------------
> Gee I hate the words floc/defloc. Generally, mix em up. I shall
> prefer the word "aglomerate" instead. When Na+ ions are in the glaze
> water, they will agglomerate the glaze solids, clayey stuff mostly, and
> cause the particles to clump together and settle rapidly to form a hardpan
> (because of attraction by electrical forces). The Epsom Salts, put in the
> water before adding the solids, slows down the agglomeration of the glaze
> solids and so prevents formation of hardpan. The Mg++ ion from Epsom Salts
> manages to do this by competing with Na ion for chemially active sites on
> the large particles of glaze material, generally getting there first, and
> so modifies the attraction.
> Thanks for noticing my goof. Be good. BFN. Peace. Tom.
>
> Tom Buck )
> tel: 905-389-2339 (westend Lake Ontario, province of Ontario, Canada).
> mailing address: 373 East 43rd Street,
> Hamilton ON L8T 3E1 Canada
>
> On Sat, 23 Oct 1999, Ron Roy wrote:
>
> > Hi Tom,
> >
> > I think you mean the CMC defloc'd the glaze - and the Epson floc'd it -
right?
> >
> > R
> >
> > >----------------------------Original
message----------------------------
> > >CP:
> > > Unfortunately few advisers give the full name of CMC, namely,
> > >Carboxy Methyl Cellulose Sodium Salt, and the liquid form of CMC would
be
> > >fully ionized, ie, Na+ ions and CMC- ions. So when you added it to your
> > >glaze slurry, boom, the Na+ ions floc'd the glaze and floc'd it hard.
To
> > >prevent this happening, always add Epsom salts to the galze water --
10 -
> > >15 grams per kilogram of glaze solids. Epsom Salts, or Magnesium
Sulfate,
> > >supplies Mg++ ions and SO4-- ions. The Mg++ ions do combine with the
glaze
> > >particles but they do not cause full flocculation, only a first stage
that
> > >thickens the glaze a bit, and the particles largely stay in suspension,
> > >settle slowly to a soft mush. The Mg++ ions then effectively keep most
of
> > >the Na+ ions away from the glaze particles.
> > >
> > >Tom Buck )
> > >tel: 905-389-2339 (westend Lake Ontario, province of Ontario,
Canada).
> > >mailing address: 373 East 43rd Street,
> > > Hamilton ON L8T 3E1 Canada
> >
> > Ron Roy
> > 93 Pegasus Trail
> > Scarborough
> > Ontario, Canada
> > M1G 3N8
> > Evenings 416-439-2621
> > Fax 416-438-7849
> >
> >
>
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