The problem with any kind of face mask, including of course gas masks, is that the wearer’s breath fogs up the lenses very quickly unless some precautions are taken. When a person breathes out, their breath is both warm and contains a high moisture content. When this hits the cold eyepieces of a gas mask this condenses and forms a fog that hinders vision. To counter this World War Two British gas masks came with a number of different anti-dimming kits, tonight we are looking at one of the most common:A 1935 pamphlet on anti-gas training explains why anti-dimming compounds were needed and their use:

The anti-dimming outfit

The respirator facepiece is designed so that the fresh air breathed in passes over the inner surfaces of the eyepieces. This reduces the amount of moisture which condenses on them when breathing out, but it does not entirely remove the condensation, except in the most favourable of conditions. Anti-dimming compound is therefore applied to the insides of the eyepieces, the purpose of which is to cause the moisture to form, not a mist, but a clear film which does not interfere with vision. The correct application of anti-dimming compound is an important part of the respirator drill, and careful attention must be paid to it.

There were a number of different anti-dimming tins in use during the interwar and WW2 period, this example is a Mk V. The pamphlet explains further:

The outfits, Mks IV and V, consist in each case of a cylindrical metal box with two screwed caps; in one end of the box the compound is contained in a metal cup:while the other end of the box contains the cloth:For convenience of identification the end of the box containing the compound is coloured red in the MkV, and in the later issues of Mk IV.

The methods of application of the different marks of anti-dimming compound are printed on the various boxes:As can be seen this tin dates from May 1940 and the tin was made by P.C. & Co. The makers initials are also embossed into the two end caps:Sadly, as is so often the case, I have not been able to identify the manufacturer. These little tins are very common as they were produced in their millions and one should not set the collector back more than £5. Check the dates however, as very similar sets were issued with respirators for many years after the end of the war.