If the bichromate is still orange it is ok. I have solutions made up well
over 10 years ago when I made my first gum that are still fine.
The gum will however not keep without preservative. However signs of
mould are usually obvious (and it goes more runny).
And of course mixtures of gum and bichromate don't keep at all.
Peter Marshall
petermarshall@cix.compulink.co.uk