Mid century chairs - what's the finish?

Hi, I'm looking for some help matching an old finish. We've had four of these chairs for years now, but then I built a new dining table so now we need more! I found four on ebay for an absolute bargain, but they were rough as guts, and had been painted. I've started stripping them back to bare timber and now need to start working out how to match the original finish.

In the photos you can see a stripped chair next to a chair with the finish we want to replicate.

The finish looks like watered-down brown paint - as in it mostly covers the grain, but not completely (see the second photo for a close-up).

Can anyone give me some suggestions as to how I can get these looking the same without having to strip my original four chairs as well please?

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