To be more precise I meant skill sub-sets; within item crafting skill-set there are mini-trees of skills: prop, decoration and item crafting. If its under item crafting I will need 2nd level of it as I learnt 1st level already. If I learn that skill and nothing happens, I will have to test which of the other two (decoration or prop) can unlock glass.
Never mind anyway - you have enough on your head I guess and when skill description comes in it will get easier to find out what needs to be learnt.
Thanks for your time and patience.