It would seem that 'finché' alone means 'while', whereas 'finché non' means 'until'.
I answered "we look at the soup while it boils" just now, and it was accepted :)
I am confused .. I have consulted my COLLINS DICTIONARY re the meaning of finche; it gives the options of 'as long as', which I understand to mean 'while, but whenever I use it in Duolingo I am marked down. I'd appreciate help!
As far as I know, this should be translated as 'while it boils', whereas 'finché non bolle' means 'until it boils'?