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Water glass

browsed through a book today that I hadn’t looked at for a long time.
It’s “Indian Jewelry Making” vol. 2 by Oscar T. Branson, copyright
1979. It has a section about cuttlebone casting. Before pouring the
metal, the interior of the cuttlebone was coated with a thin solution
of borax, water glass and water. The photographs showed the
difference between using this mixture and not. It seemed to really
preserve the mold through more than one pour. I have no idea of what
water glass is. I know that it used to be used to preserve eggs
before refrigeration and that 's it. I have seen it on drugstore
shelves in the distant past. I wonder if there are harmful fumes
released when it is heated? John, how about an answer?

Marilyn Smith

Water Glass is Sodium Silicate and can be purchased from numerous
places. The local ceramics supply sells it; Aamaco American Art
and Clay Co Indpls IN Dan Wellman

I remember having this in my chemistry set as a kid (1960-ish) -
Sodium Silicate, it was a viscous clear liquid. Only practical use,
other than as a catalyst, seems to be egg preservation. If it’s
food-grade you would think it shouldn’t be toxic when heated, but
consult the MSDS if in doubt. Apparantly it is still available:

Jim Marotti
Lancaster, TN

Hi Marilyn,

“Water Glass” is an old-fashioned name for sodium silicate. Another
common name for this chemical is “silica gel”. In the past it was
often used as a concrete sealer, and as an ingredient in
pharmaceutical products.

The most common use for sodium silicate is as a dessicant. (You’re
probably familiar with it in the form of little “don’t eat” packets
and cylinders, which absorb the excess moisture in pill bottles. Ask
your local pharmacist to save them for you. Pharmacists throw them
away by the dozen.)


You rang Modom? Water glass is a very strong solution of sodium
meta silicate. I would think that since cuttlebone is a calcareous
material, the outer parts of it would be converted to calcium
silicate which is not so crumbly. This is what occurs when eggs are
immersed in it; it gives them a siliceous coating that is impervious
to air, and so they don’t go rotten so quickly. it increases the
strength of the shell too. I cannot see that there would be any
deleterious fumes other than the burning off of the cuttlebone’s
organic material by hot metal.

Another use for waterglass is to coat cement or concrete with it to
make the surface more impervious to the carbon dioxide solution that
comes dissolved in rain and eats it away over the years. Another
but similar use is that if you have a concrete tank which leaks, put
on a pair of rubber gloves, pour some cement powder into one hand,
pour a little water glass into a hollow, mix as fast as you can and
ram it into the leak for it will set hard in just a few seconds,
even under water. – Cheers for now, John Burgess; @John_Burgess2 of
Mapua Nelson NZ

Not exactly true. Silica Gel is a Gel which is formed by
reacting the silicate with an acid.

Sodium silicate is used as an adhesive and also as a Sand casting
molds and cores. In the core process CO2 gas is the acidifing
agent. It is also used in a resin based mold system with an acidifing
resin. The best place to buy it is from a ceramics material
supplier. Jesse

Hi, all- In addition to egg preservation, in days of old sodium
silicate was used to stabilize turquoise.

Lee Einer

I’ve used a 50/50 mix of sodium silicate and water to coat my tufa,
investment and cuttlebone molds for many years. I’ve never added
borax to the mix, but I can see how it might make the surface
smoother and perhaps provide an additional element of protection from
hot metal. However, from my experience, several thin coats of the
sodium silicate/water mix keeps the molds from deteriorating so you
can use them repeatedly. Larger molds tend to deteriorate more than
smaller ones, as the mass of molten metal holds its heat longer. In
the U.S. Southwest, these molds are passed down or traded.

Generally, your original casting is traditionally done in bronze.
This casting is finished and used for sandcasting, or for impressing
into another tufa, investment or cuttlebone mold. The original is
always kept as the master. Many of the prefabricated 'sandcast’
models you see advertised are from pieces bought in the '70’s from
master carvers.

A Material Safety Data Sheet for water glass (sodium silicate
solution) is at

Related including more synonyms than are in the MSDS,
is at

Some people also use “water glass” for a compound of potassium
silicate. - for example:

Other people consider the potassium compound to be potash water
glass - for example: which has
on potassium and calcium compounds related to sodium
silicate solution in a Glossary of Materials used in 19th and 20th
century Plaster Architecture.

Dan Kamman