A

Unique

One or two examples only known, lamps in this category may be prototypes, patent types that never saw general use.

Upton and Roberts, Cryptograph Lamp.

B

Extremely Rare

Handful of examples, majority in museums. Not generally available. Do not generally come to market. Only present in the largest or long standing collections.

Sight lamp Davy and Improved Clanny. Side filler Stephensons

C

Very Rare

Only a few examples known (say  up to a maximum of twenty), but only found in larger collections. Not generally available.

Newman Davys, Columbus, Clowes, Stephensons (Improved). Different type Donalds.

D

Rare

Numbers of examples, to be found (in excess of twenty known) with perseverance. Medium size collections having an example.

Normal Donald, Jack lamps, Standard Davys. Routledge and Johnsons. Ashworths, Protector CT33

E

Common

Generally available at moderate cost within a few weeks. Often seen on ebay. Example in most collections.

Davis Kirby, Davis Boss, Patterson High Candle Power. Protector CT33A

F

Very Common

Available generally on ebay, antiques markets and the like. Not generally regarded as ‘collectible.’

Protector GR6S, SL, Hailwood O1