DUST PREVENTION Dust is often a great trouble in photographic work, both in the field and in the work-room. Dust in the camera and on the lens is the most frequent cause of trouble, hand cameras being more prone to the defect than others because of the usual practice of carrying them unprotected. Dusty lenses cause flat and misty pictures. Dust will find its way into the lens through the slits used for Waterhouse and rotating diaphragms, and the only preventive is to fit, when possible, a band of velvet ribbon round the lens tube to cover up the slots as much as possible ; in the case of Waterhouse diaphragms the band may be kept completely over the slot when the diaphragm is not in use. Rubber bands have been recommended, but these contain substances that tend to mark and discolour the lens mounts. The plate-changing arrangements in hand cameras, and shutters working inside, are often the means of stirring up dust which settles upon the lens and plate. Frequent dusting of the in terior of the camera and plate sheaths is advis able, but unless done carefully more dust will be deposited than removed. Coating the inner most parts of the camera with glycerine or vase line has been suggested; such a coating will naturally hold down the dust and prevent its flying about, but inasmuch as it is liable to be come messy and to need frequent changing, the method is not recommended. The focusing screens of stand cameras are occasionally thinly coated with vaseline in order to make them more transparent, and the coat serves as a kind of trap for the dust ; in this case the cleaning is quite easy, but the cleaning of the interior of the bellows is quite another matter. Dark-slides invariably attract dust, but they can easily be dusted, and any coating of grease might inter fere with the sliding shutter or find its way to the plate. Dark-slides having draw-out shutters
are the greatest offenders ; the light-trap at the top of the slide, which closes the aperture when the shutter is completely withdrawn, is made usually of either velvet or rubber, and this scrapes or wipes the dust from the sides of the shutter as it is drawn out and returned, thus in time forming an accumulation. Thorough dusting of the light trap and the interior of the slides is an obvious remedy. Dust settling upon the plate causes many spots, and it is of but little use dusting a plate before putting it into the dark-slide if it is to be exposed to a minia ture dust storm in the camera.
Plate dusters are articles of commerce, but if they are not kept scrupulously clean they put more dust upon the plates than they take off and do more harm than good. Plates rarely need dusting with a brush ; when taking them from the box or dark-slide, a gentle knock with the edge upon a table will do all that is neces sary. Of dusters, an old well-washed silk hand kerchief is one of the best.
Frequently unsuspected resting-places for dust are the top rims of bottles and the crevice between the cork and the bottle neck ; before pouring a developer from a bottle, the rim and mouth should be wiped, otherwise any accumu lated dust may find its way to the plate and cause spots. The corks of bottles should be kept covered with a paper or cardboard cap.
Many professional dark-rooms and all plate making rooms have their floors kept damp in order to prevent dust.
The utmost care is necessary when mixing chemicals, more particularly pyro and other developers, to prevent small particles of the developer in the form of dust flying about the room and settling upon sensitive surfaces.