what is wet folding?

[FrumiousBandersnatch]

Firstly, I'll direct you to the gigantic thread about MethylCellulose.

Secondly, since direction is rarely followed, I'll say that you probably want to stay away from buying the stuff in a stationery store, bookbinder's supply, or art/craft store. This is simply because the cost/amount ratio is very skewed. (10 USD for an ounce or so of the stuff...I have no idea what the grams are for that) At a hardware store you can find a lot more for a lot less money.