Amber is very pretty and makes good gambling chips. Using amber as a gambling stake also means it changes hands an awful lot… which is what the Rubbery Men are after. They trade it and gift it because of amber’s special property; it’s kind of like a sponge. A sponge that absorbs (and stores) Vital Essences, which are basically what they sound like. Life force, basically. You aren’t likely to die from handlin amber any time soon, because it’s a pretty gentle effect. Rubbery Men can then use that amber to mould and shape flesh, letting them take on forms that are closer to human than the squid-faces that currently walk London’s streets.