I printed quite a few different papers with gum without sizing with
reasonable results.
One of the favourite British papers for gums was 'Bockingford'
Watercolour paper. This is an internally sized colour stable mould-made
woodpulp paper with a not surface.
I would expect most gelatine tub-sized paper also to work for single
coating without sizing. Velin Rives BFK is only very lightly sized I
think.
For multiple coating you need to soak and dry the paper before the first
coat to avoid changes in dimension. After the first coat you do need to
size - I used a weak solution of Rabbit Skin size applied warm with a
brush.
Never found a really good black!
Peter Marshall
petermarshall@cix.compulink.co.uk