Re: gum mixes
Yup I use lumps too (from the Grand Bazaar in old 'Stanbul). I'm not so precious with it though.) I soak 500 g in a litre of cold water and then have at it with a hand held kitchen grinder/grater thingy. Strained through a nylon stocking adds a certain glamour and removes the debris. The result is a beautiful light straw liquid to which I add 100% Thymol soln. (10 drops or so).
For the mixture I use 5 ml saturated Pot Dich + 5 ml water + 10 ml gum + varying amounts of pigment depending on layer, colour etc..
I tried using some gum powder from a supplier in the UK but the solution looked so ugly I couldn't bring myself to use it! Go Lumps!