Silver nitrate reacts to the salt deposits in sweat. While this component is not as durable as amino acid (see ninhydrin processing) it is more likely to yields a result that using processes which rely on components such as fat for the reaction process (see iodine processing). Silver nitrate is a sprayable solution of silver nitrate and a carrier such as water or alcohol. Silver nitrate should be mixed in a 0.3% solution which means four ounces of silver nitrate to one gallon of water. An alcohol solution can be made by mixing 4 ounces of silver nitrate, 4 ounces of distilled water and 1 gallon of 190 proof grain alcohol together. The alcohol based solution offers a faster drying time than a water based solution but there will be some loss due to evaporation. Naturally there is a fire hazard associated with the mixing and final solution of you use the alcohol type. Processing with silver nitrate is a two step process. First you subject the item to be printed to the solution by either spraying a good consist layer of silver nitrate on the object or by dipping the object in a tank of silver nitrate solution. Once this is done the object should be exposed to a carbon vapor light. If no such light is available the exposing the object to sunlight will work just as well. Obviously if you do not have a carbon vapor, or an iodine cobalt light, then you are going to have to expose the object to direct sunlight. Since this may be the case this is a limiting factor in that you can only process items which you can either carry out to be exposed to the sun or items which are already exposed. Two things about silver nitrate. First, this process should be done last if you plan on conducting a ninhydrin or iodine test as silver nitrate will remove the amino acid and fat components required by these other tests. The second issue is that the object should be allowed to dry before exposing the object to the light source. There is the potential for over-development so the exposure to the light source should be monitored closely at all times. Once the prints have developed they should be photographed and promptly removed from the light source. A few words of caution! Silver nitrate can be used on most of the same items that iodine and ninhydrin can be used on. This includes many wood products including untreated wood, plasterboard, wall board, some types of leather, drywall, paper products, some types of house sidings and so forth. It is a good process to be used after the ninhydrin or iodine processes and may yield an identifiable impression. |
