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Photographs of jewellery fall into two distinct categories; real
jewellery and imitation, or costume, jewellery. Imitation jewellery is
photographed for pictorial or catalogue purposes only, so it is easier
to deal with, presents no special technical difficulties and can be
handled by the ordinary studio.
Photographing real jewellery, because of its extreme value, is highly specialized work. There are many uses for such photographs, but it is a fairly limited market for photographers. First, because jewellery of this expensive class is also frail, jewellers are not very keen to let it be taken away from their premises. Most of the really important jewellers, in fact, have a photographic department on the premises run by their own photographic staff. Some set aside a room for the use of an outside photographer who may keep his own apparatus set up in position for use at any time.
A knowledge of gemmology and the crystallography and structure of precious stones is a great advantage for the photographer.
Jewellery in this category is photographed for many purposes apart from the pictorial and advertising interest. In one large firm all jewels that are regarded as important new creations are photographed so that the pictures may be interchanged between the various branches all over the world, so that designs and trends may be maintained at a high standard. Albums of these photographs are kept in the showrooms to assist clients in choosing designs around which their old and out-of-date jewellery can be remodelled. The photograph of the original jewel before remodelling can be of great assistance to the designer when making up the new design. Photographs are taken of these original jewels to keep a record of the stones before they are unmounted in case of any dispute afterwards.
Important jewellers hold photographic records of all pieces of jewellery made by them to hand to the police in the event of loss or burglary.
Photographs are also taken of large and specimen stones on offer in the London or other markets. These are then sent to overseas branches for the consideration of likely purchasers as it is not advisable to keep sending stones backwards and forwards unless something definite is demanded. An X-ray photograph is sometimes taken of a pearl where there is a doubt about its being cultured. The pattern on the film caused by the deflection of the rays shows at once whether it is genuine or not. Photomicrographs taken of faults and inclusions enable a stone to be identified. Stones have actually been identified in a court of law by means of such a photograph taken years previously. A gem is often identified solely by photographs, and photography does provide a useful supplement to the normal records kept by the jeweller of each important stone.
Photographs are taken from a number of angles, including plan, from behind, and side views. These photographs are printed the same size and attached to the record. Enlargements may be made to indicate precisely the position of flaws and surface imperfections, and in some cases photomicrographs are made of superficial irregularities with the stone immersed in oil. The oil, which is highly refractive, creates an intense black line around the edge of the stone, clearly outlining the shape of the indentation.
Another photographic means of identifying stones is to record the pattern produced on a sensitive emulsion when a narrow pencil of light falls on the stone from a given angle. An extension of this method is to record the pattern of fluorescence produced by the diamonds in a piece of jewellery exposed to filtered ultraviolet light.
Diamonds are sometimes coloured artificially by exposing them to the radiations of radium. Where this has been done, it can be detected by putting the diamond in contact with a photographic plate in the dark for a period of several hours, if the stone has been radium treated, an image shows on the plate. X-ray records are also used to identify the details of the mount in which the gems are set.
Jewellery designers make considerable use of photography for enlarging or reducing a design, thereby saving themselves hours of work.
Jewellery is usually photographed same size- as it loses a certain amount of definition and brilliance if enlarged. The best camera for this work is a 8 x 10 ins. process camera on rails mounted on trestles. A vertical easel covered with thick lino is used for pinning up jewels for photographing because they are displayed to better advantage hanging than lying flat.
An 18 inch process lens is used as it is essential to have a long focus lens to keep the camera well away from the jewels and so allow sufficient space between lens and easel for manoeuvring the lights. A vertical set-up on the principle of a copying camera is also useful for jewels that have to be laid down flat.
For general and perspective work, a whole plate stand camera with color-corrected anastigmat lens is used. If it should be necessary to reduce the size of a jewel in taking the photograph, the amount of reduction is kept to the absolute minimum.
The most suitable type of illumination is given by a floodlight with a general diffusing type of reflector, fitted with a 1500 watt tungsten light. A pointed or concentrated light certainly does not give as good results.
When lighting jewellery, the main source must always be supplemented with reflectors to fill in dark hollows in the stones which would otherwise debase their apparent quality. Small movable white reflectors on stands, adjustable white roller blinds on two sides opposite the light and a large white card reflector around the lens are used to highlight the reflecting surfaces of the jewels.
The main light source shines at an angle of 45° on to the subject.
Most coloured precious stones, such as emeralds, rubies and sapphires, reproduce darker on orthochromatic emulsions; and stones are usually more valuable when the colour is deeper. For this reason ortho films are often preferred. But a panchromatic emulsion is used when a fault or inclusion is to be photographed.
The detail and beauty in stones is always more apparent when the background is kept simple. A fine-grained linen paper (of a suitable shade) is generally sufficient.
To avoid shadows which may obscure the detail of the delicate mountings, the piece may be fixed to a sheet of glass with cellulose cement. The glass is then supported a few inches away from the background.
The finished print is made on a brilliant black-and-white bromide paper and is always glazed to add sparkle.