Can I use sodium silicate waterglass to cast a glass object?

[Christofer Br]

Waterglass is sodium silicate dissolved in water that upon drying forms soda glass. Could it therefore be used to cast a glass object like a slab or will it not form nicely?

 

[anorlunda]

Crystal gardens[edit]
When crystals of a number of metallic salts are dropped into a solution of water glass, simple or branching stalagmites of coloured metal silicates are formed. This phenomenon has been used by manufacturers of toys and chemistry sets to provide instructive enjoyment to many generations of children from the early 20th century until the present. An early mention of crystals of metallic salts forming a "chemical garden" in sodium silicate is found in the 1946 Modern Mechanix magazine.[24] Metal salts used included the sulfates and/or chlorides of copper, cobalt, iron, nickel, and manganese.

Pottery[edit]
Sodium silicate is used as a deflocculant in casting slips helping reduce viscosity and the need for large amounts of water to liquidize the clay body. It is also used to create a crackle effect in pottery, usually wheel-thrown. A vase or bottle is thrown on the wheel, fairly narrow and with thick walls. Sodium silicate is brushed on a section of the piece. After 5 minutes, the wall of the piece is stretched outward with a rib or hand. The result is a wrinkled or cracked look.

It is also the main agent in "magic water", which is used when joining clay pieces, especially if the moisture level of the two differs.[25]

 

[Nik_2213]

It's been a while, but I've used sodium silicate 'water glass' both for 'crystal gardens' and egg preservation.

IMHO, 'water glass' is much too brittle for use in casting. Worse, it is sufficiently alkaline for 'manual handling' issues.

( And Sufficiently alkaline to eat through an aluminium pan... )

FWIW, I don't know if any-one has tried glass-fibre reinforced 'water glass', but I'd expect even quality fibre mat, as used in GRP boat and car etc repairs, may have a colour taint, plus sufficiently differing refractive index to not be transparent as requested...

I'm sorry, I'm told 'clear-casting' with acrylic resin is probably the better option. How you get the bubbles out remains beyond me...

 

[Tom.G]

How you get the bubbles out remains beyond me...

A) Be careful in pouring into mold to not mix air in the liquid... as in pour gentle down the side of the mold
B) Deaerate if needed

• Vibrating the filled mold may be sufficient with low viscosity liquids
• Put in vacuum chamber... doesn't have to be fancy, for small items such as will fit into a canning jar, a hand operated vacuum pump may be adequate.

(This is not applicable in your case, included here for completeness)

• If it's a two-part compound: Mix as you would mix car repair Body Putty. Don't stir, smear out on a flat surface with a spatula, fold the layer over itself, repeat.
• If bubbles are not real critical in final product, just letting it sit for a few minutes after mixing may be sufficient; depends a lot on viscosity.
• If bubbles are critical, put in a vacuum chamber after mixing; may have to repeat after pouring into casting mold.

Cheers,
Tom