Grampahans,
Exactly. Many British military firearms were treated the same way. Kit Ravenshear, who built and restored many, many British military flintlocks describes the process very nicely in his little books. He does suggest that raw linseed oil drys harder but obviously takes much longer to dry.
dave
That really is not accurate in regards to raw linseed oil.
Raw linseed oil never really dries. It forms more of a gel.
The boiled oil of commerce prior to WWII was a deep ruby red color. This did not give a red finish on a stock in thin films. More of a pale orange appearance.
Linssed oil boiled with lead forms a leather-like film on whatever it is applied to. Boiled oils prepared with manganese or cobalt driers give high gloss films with hard surfaces.
Boiled oils prepared with lead tend to darken with age. How much they darken will depend on how much lead was "boiled" into the oil. It is possible to get up to about 1% lead by weight of metal to oil weight. Generally you would see about 0.5% lead in a boiled oil prepared the old way.
Generally, those stocks finished with a boiled oil high in lead, up around the 1%, will usually turn almost black on the surface. As the oil film dries on the wood the "spent" dryer metal is kicked to the surface of the film as it dries. On the surface it will react with sulfur-bearing gases in the air to form lead sulfide in the surface of the film.
Some things on boiled oils and dryer metals.
Lead is a "through" dryer. As the applied film picks up oxygen from the air it will migrate down through the film. The film dries at a nearly uniform rate from the surface to the base of the film. Manganese and cobalt are surface dryers. The film dries first on the surface and then the drying reactions proceed down through the film. Since the dry surface tends to slow down oxygen pick up by the film the base of the film takes a lot longer to dry compared to the surface.