I recently purchased an antique oil painting (18th century), whose frame has a very particular smell that I had never smelled before, touching the frame imparted a fair degree of grime onto my hands, but the smell is not like any grime I've smelled before. It's a very unusual smell that I can hardly describe, it's pungent, however not entirely unpleasant. I wouldn't want to be subjected to the smell continuously, but a rare whiff of it is pleasingly unique.

A cursory google search seems to want to tell me that this is simple "antique mildew", but I wouldn't describe the smell as mildewy or really even associate it with decay rather than age. It seems like a rather inert smell, seemingly not too noxious to breathe, but ingesting something that smelled like this would surely give you a stomach-ache or worse. It's not quite "sour" (but almost) or "chemical", but if you told me it was a wood finish that had long ago "turned" or oxidized, I would not be surprised. However I am not familiar with the normal scents of most wood stains and finishes, let alone antique ones.

I was content to let this mystery lie, as I didn't feel it necessary to mitigate or remove the smell of the painting (it is a part of the painting's patina, after all), but a few weeks later I purchased a vintage (possibly antique) wooden mortise gauge for woodworking, and it had the ***exact*** same smell, but much stronger, the gauge is basically the same shade of darkish brown wood stain, but as I'll be using it with my hands I wanted to clean it off, whatever it may be. Especially as the smell will linger on the hands until a vigorous scrubbing. And the gauge doesn't seem to slide as well as would be expected, possibly due to this grime building up.

I'm sure to remove it I could just try increasingly rough cleaners, and at worst sand and refinish the gauge. But more than anything I'd enjoy precisely identifying the smell. I realize identifying smells on the internet is difficult, but as the next outlet for identification is shoving pungent antiques under the noses of people more learned than myself, I figured I'd try the internet first.