In a similar manner that Tom describes except that on the Ratner the letter lock is some distance from the keyways and has to operate via the vertical curved bar I illustrated.
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I'm at differerence with you on this Parautoptic. As I see it the closing of the keyway by a shutter was part of the original specification and solely intended to make the safe resistant to explosive attack, firstly gunpowder then high explosives. The Chatwood Treasury was particularly effective against this latter form of attack.
On the other hand Dual Control was originally known as Partnership locking which adequately describes the system and which would be incorporated n the original design specification.
The earliest wrought iron security cupboards as they were know before fire-proofing were
usually fastened by wheel locks and box-of wards locks which with their large keyways were very vulnerable to gunpowder attack.
The only defence against this was the lockable escutcheon with a compact Barron lock in a casing with chamfered edges to resist sledging. This by design could also be described as dual locking but not necessary the intention.
Later in the century brass escutcheon locks were commonly used incorporating very small lever locks. The application was probably as a retro-fit on single lock safes where dual control was later considered desirable against acts of collusion.
Dual control was also available within a single lock of course.
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Safeman, I think we are at crossed purposes here. The comment about the container with a less secure lock was referring to the blisters that MOD used to use, and may well still use, over a keyhole.
The combination blisters absolutely were for that purpose. Obviously the best thing with confidential material is that it is never seen by anyone who is unauthorised. Next best thing is if they have been compromised, you at least know that this has happened.
[QUOTE=Chubby;28417]Safeman, I think we are at crossed purposes here. The comment about the container with a less secure lock was referring to the blisters that MOD used to use, and may well still use, over a keyhole.
Could be right Chubby. Thought the subject was keyhole shutters.
My fault for taking things off topic.
If the Chatwood is easily drillable it would be to facilitate a lesser level of dual control against sarupticious entry but it it was hardened then it would be anti explosive. Of course if it was hardened it would do both.
Sometime I will try drilling the sliding obstruction and if it was easy we will know that it wasn't against forced entry.
interesting line of enquiry!