MIMF

I bought a house in Chicago built in 1895. Window and door trim is stained oak (dark) with a finish where the pigment seems to have separated and grouped together in little pebbles. I originally thought it was shellac but denatured alcohol doesn't do much. Any thoughts on what the finish might be? Will try to post a photo tomorrow.

It could be an oil varnish.

A picture would help.

It could be that the finish (most likely oil) on top of a sealer of shellac, has shrunk over the last century.

It may be that further coats of varnish have been applied over the years. As the varnishes shrink, they leave little cracks sometimes. The next coat fills the voids, and perhaps gives the appearance you are describing.

Are you wanting to remove the varnish and refinish?

Are you wanting to "improve" the appearance, or seal the wood, or maintain the vintage look?

Here are a couple photos of a door.

It looks like varnish with mold growing under it. Notice the raised grain. That door was really wet sometime in its life.

I don't think it has any mold.

I think the original coatings lost the solvents, shrank back and later coats were applied.

Again, the question of what do you want to do with this?

The wood looks solid and sturdy underneath.

I think you could strip the doors easily, refinish and have a great looking and very solid door.

I don't think it's mold either. The dark spots are hard and fly off in granules when I dry scrape with a putty knife. There appears to be more varnish under the dark spots, so I think the wood is well sealed. It looks pretty good with the dark spots removed. I'm wondering if someone put on a varnish that was not chemically compatible with the one already on so it separated.....?

What do I want to do with it? I want to get rid of the dark spots so the beauty of the wood can be seen. Was hoping to a product that would help remove the top layer and leave the original finish. Dry scraping is a lot of work (two story house) and very messy. I can easily remove the doors and take outside to strip then refinish. Don't want to remove the baseboard and trim because of the likelihood of lead-based wall paint in a house of that age. Don't want that type of dust flying around. Guess I'll do the trim the hard way unless I can identify a solvent that will help soften the outer layer.

Thanks for your thoughts, folks.

You have strippers which are caustic (lye) based, and others which strip with methylene chloride.

Both work, and have their problems to deal with.

Then you have the choice of using sandpaper, and scrapers to take off the biggest part of the material. Use solvents and sandpaper to smooth the surface so it will accept a new varnish coat. You can strip agressively down to bare wood, or remove the surface sufficient to get a smooth surface. and add another layer of varnish over the surface.

Edit--I forgot to mention stripping with heat guns. I don't have much experience.

Generally, I hate stripping old finish. The last time I did this was to restore a piano with a nice case.

Thanks, Steve. I'll check in to the strippers to get down to a smooth finish.

How about Citristrip - the orange oil based stripper?
I used it once (for a very easy job) and it worked very well.
This looks for more challenging - but it is a LOT more friendly than other paint stripping products I've used.

Thanks, Chuck. Good suggestion.

Here is a small section after I removed some of the ugly stuff. Thanks everyone for your thoughts and suggestions.

I'd be scraping this wood work with a sharp scraper. No lead to worry about and the old varnish just explodes off the surface. I scraped all my trim and even my floors. It was faster and a lot quieter/ less smelly than any other method I could come up with.
Could it be that the shellac has long since polymerized and can't be melted with alcohol anymore?