[Greenbuilding] linseed oil finish causing freckles?

[Chris Green]

Jim Meehan wrote:
> Anyone here have experience using linseed oil as a finish? 
I have
> <snip>
>
> The interior doors are paint-grade birch, and after the painters applied
> two coats of linseed oil, some of them (about half I'd say) started showing
> grey splotches all over -- it almost looks like mildew.
It looks like uneven absorption of the oil finish to me, caused by the 
original log being rippled inside. Grain running at angles to the 
surface will absorb stains and finishes at a different rate than grain 
parallel to the surface. If the logs the veneer was had a bumpy, rippled 
structure inside, the veneer will include both the parallel grain in 
spots and the angled  grain elsewhere.
Another term for the grain being at angles to the surface is that the 
grain has 'run-out.' .
Your veneer is like a perfectly flat highway cut through a lot of 
rolling hills.

The most famous form of this effect is the tiger-striped,  flamed, or 
fiddleback maple used in fiddles and violins.

I can't think of a simple remedy for this at this time other than 
sanding down to bare wood and refinishing the doors  by first sealing 
them with a few very thin coats of  french polish/ shellac flakes 
diluted in alcohol, or some such.

If you opt to refinish them, it might be a good idea to first practice 
on pieces of plywood left over from making the doors, if such are still 
available.

Chris Green.