planks treatment

I am interested in old boat building techniques.
Would anybody know how wood was treated for Gloucester schooners
for example.
I noticed there was no paint on those boats.
I assume that wood was treated with oil, but how, which oil and
for how long.
Another question is what is the best material to put between planks
for double planking.
Someone suggested white lead, can it be gotten now?
What is an alternative if lead can not be gotten?
Linen soaked in paint, but which paint should it be soaked in?
Any good source of mahogany for planks?