Film almost transparent

Hello,

Please excuse my poor English, I speak french.

I own a Lubitel 166B, and I've tested the Caffenol processing.

I used the classic recipe (C-H), with a 1mn vinegar+water stop bath (I
need to buy acetic acid) and a 5mn fixing using Ilford Rapid Fixer. The
result was an almost transparent film : http://hpics.li/d38c698

I tested my washing soda, and he have a 20% water. So I tested a 2nd
film, adjusting the washing soda quantity and processing 16mn instead of
15mn... for an almost identical result.

Is a transparent film a sign of a too short processing ? Must I let the
caffenol acting for a 30mn time to be sure ?

franssoa