. The silver sunbeam : a practical and theoretical text-book on sun drawing and photographic printing. ction of light on the plate de-velopes in the film, and not on Flg 20* the surface. This rule willgenerally indicate to the oper-ator in what direction to lookfor the cause. The intrusionof light may be through smallholes in the wood work of thebox, or in the bellows, or thecut off in the plate shield maynot operate, or the shield maynot fit closely in its place inthe box. If the chemicals are at fault,the causes are found in eitherthe bath or the collodion or thedeveloper. A very light col-o
. The silver sunbeam : a practical and theoretical text-book on sun drawing and photographic printing. ction of light on the plate de-velopes in the film, and not on Flg 20* the surface. This rule willgenerally indicate to the oper-ator in what direction to lookfor the cause. The intrusionof light may be through smallholes in the wood work of thebox, or in the bellows, or thecut off in the plate shield maynot operate, or the shield maynot fit closely in its place inthe box. If the chemicals are at fault,the causes are found in eitherthe bath or the collodion or thedeveloper. A very light col-ored collodion will sometimesbe the cause—the remedy isthe addition of a little tinctureof iodine. If, while using aripe collodion of a deep strawcolor, fog should occur, thefault is probably in the bath—a drop of nitric acid to eachtwenty ounces of the bath willbe sufficient in case the bath has been neutral. If this doesnot remedy the fog, the cause may be organic matter in thebath. The remedy for this is to neutralize the bath withbi-carbonate of soda and allow to stand in the sunlight until. 546 DEFECTS AND REMEDIES. all precipitation ceasesand the bath has becomeclear. Then filter and trya negative. A little ni-tric acid may be needed. Unclean glass is fre-quently a cause of fog :this can readily be de-tected by its appearance,as it is always found be-tween the collodion andglass. Hard rubber bathssometimes contaminate asilver solution. Beforebeing used they shouldbe cleansed by using astrong alkaline wash, andwhile being used the sil-ver solution should neverbe left in, but should bepoured out and the bathwashed as soon as thedays work is done. Lime water, rain watercollected from the roofsof houses, and water containing alkaline salts, if used in thedevelop, may cause fog. The vapor of ammonia, or the presence of sulphuretted hy-drogen, will cause an undue depositof silver on the plate. Fogging is sometimes caused byremoving the glass from a coolplace and taking it in
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