SOONER or later someone is going to come into your studio to have some portraits made and when your printer makes the proofs the subject is going to have a couple of black eyes.

This is stating the effect before the cause but if it serves to get your attention we are quite sure you will be interested in the cause so that you will be able to avoid the trouble.

The black eyes will be caused by your sitter wearing a pair of eye glasses or spectacles the lenses of which have been made from Crookes glass. The lenses may seem to be perfectly transparent or they may have only a slight smoky color. They will not be amber colored - in fact will not have sufficient color to make you take notice of them but they will very likely produce the result we have mentioned above.

Now for the cause.

Sir William Crookes who invented the Crookes Tube invented this glass primarily for the use of laboratory workers who might of necessity be exposed to the very disturbing effects of ultra-violet rays which are an invisible constituent of light.

The Crookes lenses absorb ultraviolet and as the ultra-violet in sunlight produces a certain amount of eye strain or fatigue Crookes lenses are being recommended by opticians to people who spend a great part of their time out in the open in bright light, on the water, motoring, etc.

As a photographic film or plate is especially sensitive to ultraviolet rays you can readily see that if a sitter is wearing these glasses the light reflected into the camera from all of the face, except that part directly back of the eye glasses, will contain the ultra-violet while the light reflected from the eyes through the eye glasses will be minus the ultraviolet. So the eyes will seem to be under-exposed.

Portrait Film Negative, Artura Print By Sidney Riley Sydney, Australia.

Portrait Film Negative, Artura Print By Sidney Riley Sydney, Australia.

The effect will be very much the same as if the sitter were wearing tinted glasses. Crookes lenses are made in two grades, A and B, the A glass having practically no color at all and the B glass just the slight smoky appearance we have mentioned.

If you encounter a subject wearing the A lenses you may not notice the effect in your negative, especially if you use artificial light for negative making. But if your sitter wears the B lenses, look out for trouble. The most simple remedy is another pair of lenses which the sitter usually owns.

It is interesting to know that these Crookes lenses also absorb infra-red rays which are found at the opposite end of the spectrum from the ultra-violet and which are also invisible.

These rays are given off largely by hot metals or glass and often cause defective sight, especially among glass blowers, in the form of cataracts on the eyes. The Crookes lenses offer the necessary preventive measure to safeguard the workers' eyes. So they are another of the results of scientific research that are proving a great blessing to humanity.

The Crookes glass absorbs the ultra-violet and infra-red rays because of metallic oxides and nitrates that are used in making the glass. One of the most common of these is Nickel Oxide, there being several different formulae, all producing very much the same effects.

As we said at the beginning, however, the thing that will interest the photographer most is the way these eye glass lenses will act as filters when a subject is being photographed. Keep this in mind and ask your sitter if he is wearing Crookes lenses if you are at all in doubt.

Study the advertising pages of good magazines and you will find examples of a new and distinctive style of commercial photograph that is being made to sell merchandise. They are what we would term, portraits of merchandise. You can make them and you can sell them.

Portrait Film Negative, Artura Print By Sidney Riley Sydney, Australia.

Portrait Film Negative, Artura Print By Sidney Riley Sydney, Australia.