What kind of key for this old door (mortise lock)? - Home Improvement Stack Exchange

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

lock - Can I repair and rekey this salty security door? - Home

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How to change locks on front door with old handle-set? - Home

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How to Make Keys for Old Mortise Locks

Cant figure out what type of lockset to buy for this bedroom door. : r/ HomeImprovement

doors - Options for replacing mortise lock with keyless lock

Key stuck halfway in door lock - Home Improvement Stack Exchange

Is it possible to replace the lock on this door that has been

Plantex Heavy Duty Door Lock - Main Door Lock Set with 3 Keys/Mortise Door Lock for Home/Office/Hotel (7086 - Brass Antique & Satin Black Matt) : : Home Improvement

Is it possible to replace just the antique locks or will I need to