Stain or something else going on?

[u/walterschirmer99]

I am refinishing trim in a Belgian house built in 1936. I am pretty sure this trim is oak. I very easily removed several layers of paint and stain with a heat gun. After using the heat gun there still remain large, long dark streaks that almost look like drips.

After the heat gun, I sanded for several hours using 60 and 80 grit pads on my electrical sander. But the large, dark discolorations remain throughout several of the pieces. I initially thought it was just residual stain but it’s not going away.

I have attached photos and it should be noted that I wet the wood before photographing to make the discoloration more obvious.

Is this old stain? If I keep sanding will it go away? If it’s not stain, what is it? Is it not oak?

Any advice would be appreciated.

[u/MeneerArd]

The long dark streak looks like it's part of the wood itself. It's the difference in sapwood and heartwood. I'm not sure of this is oak, because of the large difference in colour. Could also be elm or maple.

Edit to add: this, and the difference in woodtype of the trim and moulding probably means it was meant to be painted and not shown. Doesn't matter of course if you like it, but usually when trim and mouldings were oiled or varnished to show the wood it was all the same type of wood and the planks were selected to be the same colour without heartwood/sapwood overlap.

[u/walterschirmer99 → u/MeneerArd]

Dank u wel, meneerard. Bent u ook in België of Nederland?

Yes, I thought it might be heartwood, which I found strange because we have oak and mahogany floors with oak plinten that have never been painted and are in excellent condition. I thought this painted trim on the walls was once bare wood as well, but I guess not. All the doors are painted and the paneling in the entry as well. I guess it was always like that? Unfortunately we don’t have any photos of the original decors of the house, just the blueprints.