What kind of key for this old door (mortise lock)?

Question

I am helping someone with a lost key for her bedroom (interior) door; the door hardware is probably about 100 years old. There is clearly a lock and a keyhole -- see photos.

What sort of key would activate the lock, and where would I get it? Are these precise keys that require a locksmith, or would a generic skeleton key work?

UPDATE: I got the keys and I am not sure if they are correct as the lock itself seems to be seized up, possibly from being painted over in the past. When I turn it, it moves a tiny bit (1/32") but then seems to be stuck. How can I tell if I have the wrong key or it's stuck somehow? I sprayed lubricant on it but that didn't affect it.

Answer 1

To me that looks like what we in the UK would call a "mortise lock". In the UK we would expect it to normally contain a lever lock mechanism but if it's very old or very cheap it's possible it might just be a warded lock.

Personally I would suggest removing the lock from the door and taking it to a locksmith.

To remove it from the door you will need to first remove the bar that links the two handles. To do this you will need to remove at least one of the handles. Depending on the particular design of the handle you may be able to remove just the handle or you may need to remove the handle and the plate together.

Once the bar is removed you should be able to unscrew the lock mechanism and slide it out of the door.

Answer 2

This is a classic mortise lock (residing within a pocket cut into the door's edge) operated by a bit key. It may or may not have wards (requiring cut-outs in the bit), or levers (requiring much more precise cut-outs, or absence of cut-outs) or both.

"Skeleton keys" are an attempt to guess which patterns might work with this particular lock. If you get an assortment of them, one may work the lock and you're all set. If they don't, or if you want a key which is specific to this lock (well, and locks set up identically), a locksmith can take the appropriate measurements and cut one for you, and/or diagnose what else might be wrong with the mechanism.

Lever mechanisms can be highly precise and as secure as other designs... but the ones used in old mortise locks in the US generally aren't.

("ORK Security Services -- full service locksmithing, very part time" and now decades out of practice/out of date. I still do occasional jobs for friends.)

Answer 3

You can buy skeleton keys and sets of them, sometimes dozens in a set on Amazon. Some of the larger sets are ornamental only. If this is a privacy lock, which it probably is, almost any skeleton key will work including the one with a plain flat blade sold as a privacy key. If this is a security lock there's a small chance that a key from a large set will work because it's definitely not a high security lock. It's worth a try because these keys only cost a few dollars. Otherwise just remove it and take it to a locksmith.

Edit: Adding a warning to echo a good comment above from @Moo: When you try these keys, do it with the door open because the key may work but the lock may get stuck in the locked position. Be prepared to disassemble the lock, clean, lubricate, and replace broken springs or other parts.