One of the cardinal rules for securing legible impressions is that the fingers must be dry. Accordingly, in these cases it becomes a matter of drying the fingers in addition to contending with other difficulties. Usually the skin on the fingers absorbs water, swells and loosens from the flesh within a few hours after immersion.
If an examination discloses the skin to be water-soaked, wrinkled and pliable, but intact, the first step is to cleanse the skin carefully as previously described. Next, wipe the fingertip with alcohol, benzine or acetone, waiting a few seconds for it to dry. The skin is pulled or drawn tight across the pattern area so that a large wrinkle is formed on the back of the finger, then the bulb is inked and printed.
If the skin is broken and hanging loose, but its pattern area is intact, it should be removed from the finger, cleansed and placed in alcohol or benzine (not acetone) for about a minute, then stretched carefully over the operator's finger so as to remove any wrinkles. It may then be printed.
Sometimes the skin is intact on the finger but so wrinkled and hard that it is not possible to draw it tight for inking. In this case it may be advisable to inject tissue builder to round out the bulbs for inking and printing. Should this fail, the ridge detail is photographed on the finger; or the skin is cut off, flattened between two pieces of glass and then photographed. Here, again, it must be pointed out that when the ridge detail does not show on the surface of the outer skin the underside should be examined, for many times the detail can be seen clearly. Should this be true, of course, the underside is photographed.
In cases where it is noted that the outer skin is gone and the finger is not saturated with water, it is possible to dry the surface sufficiently for inking and printing purposes by rolling the finger on a blotter. If this fails, the finger is wiped off with a piece of cloth which has been saturated with alcohol, benzine or acetone, after which it may be inked and printed.
Drying the fingers
In many instances it will be found that the outer skin is gone and the fingers themselves are saturated with water. A quick method of drying out the fingers is to place them in full strength acetone for approximately 30 minutes. The fingers are then placed in xylene for about an hour or until the xylene has overcome the reaction of the acetone. After removal from the xylene the fingers should be placed on a blotter until the surface of the fingers appears dry. They are then ready to be inked and printed.
It will be noted in this procedure that when the fingers are removed from the acetone they dry and harden in a matter of seconds. The purpose of the xylene is to resoften the fingers. After this treatment, should the resulting inked impressions be unsuitable for classification purposes, the ridge detail should be photographed.
X-ray photography
The use of X-ray photographs (radiography) has been advocated by some for purposes of recording the ridge details in decomposed, desiccated, or macerated cases. Briefly, the procedure involves the covering of the fingers with heavy salts such as bismuth or lead carbonate, in a thin, even film over the pattern area and then, by the use of the X-ray, reproducing the ridge detail. This procedure necessitates the use of X-ray equipment and a technician skilled in making radiographs. It is, therefore, an expensive operation. The results of the radiograph in no way compensate for the expense, time, and skill required inasmuch as in those cases where many wrinkles and creases appear in the fingers, especially desiccated specimens, the results have been very poor. In instances where there are no wrinkles or only a few, and where the creases are not too deep, the ridge detail is reproduced very well in the radiograph. In these cases, however, it is usually possible to secure impressions by inking and rolling in the regular way or, should this fail, ordinary photography will certainly give satisfactory results. For economical and practical purposes the use of the X-ray is not recommended.