Janet, the thing you want to ask for for water glass is sodium
silicate. Lapidarists often use it to temporarily bond rock to wooden
blocks for slabbing. In our area it is carried by the larger
pharmacies. I suspect a hardware store might also carry it.
Hope this helps.
Rose Alene McArthur
PS It might be a good idea to experiment with how much weight the
bond will stand before putting it on your precious piece. I have
unhappy memories of the time my husband mended our cast iron bed with
"liquid solder" and it failed in the middle of the night!