Advances in Fingerprint Technology.pdf

is much to be done to optimize the system. This work was supported by the
Special Technologies Program of the U.S. Department of Energy.
Diffusion Transfer
The USSS is investigating a method of transferring Ag-PD prints onto photographic
paper or film. The method is based on ideas of Dr. Edwin Land
during his development of the Polaroid transfer method. 38 The actual process
is referred to as diffusion transfer. 39 To perform the transfer, one needs two
items: receiver paper/film and an activator solution. The receiver paper/film
is a gelatin-coated material in which the gelatin contains activation sites for
silver physical development and the activator is a photographic developer
(e.g., hydroquinone) plus hypo (sodium thiosulfate). The transfer materials
currently being tested by the USSS are Kodak PMT matt receiver paper and
Kodak PMT activator. For transferring an Ag-PD print onto the paper/film,
the silver image is first converted to a silver bromide image using any of the
bromination methods. The brominated print is then placed on the receiver
paper/film and after this some activator solution is placed on the back of the
paper with the print. This is pressed with a rubber roller and then the paper
with the print is carefully lifted from the receiver paper/film. The receiver
paper/film, which now contains the print image without background, is
allowed to dry. As mentioned, if the background is printing with ink that
causes silver physical development, then this will also transfer. At present,
this project is still under development.
Fluorescent Ag-PD
The idea of converting the silver image of an Ag-PD into a fluorescent image
has enormous advantages; it strengthens the contrast of weak prints and it
removes background interference (i.e, if the background is not printed with
ink that promotes silver physical development). Thus far, there has been no
simple conversion of silver to a silver fluorescent compound. What has been
done is borrowed from photographic “toning” chemistry. In the mid-to-late
1920s, motion picture photographic scientists created ways to change a silver
image into colored images. 40 One that formed a red image involved a
rhodamine dye. At the time, the interest was in the red color product and
not its fluorescent properties. Under USSS guidance and with support from
the Special Technologies Program of the U.S. Department of Energy, Dr.
Kevin Kyle of the Special Technologies Laboratory, Santa Barbara, CA, modified
the photographic chemistry to apply it to an Ag-PD print. The resulting
print fluoresces in the furrow areas rather than on the ridges and there is no
background fluorescence. The mechanism is rather detailed 1 and is not discussed
here.