SPI Chem™ Wet Surface Replica Kit
Instructions for Use:
General Methodology
Once the area to be studied is selected, the white replicating resin is mixed with an
appropriate amount of the "catalyst" (see below under "mixing instructions"), and the now
curing resin system is spread onto the surface to be replicated. If the replicating material
has been stored to keep the components fresh, and the catalyzed resin is prepared according to
these instructions, after about 20-30 seconds on the surface, the resin will have polymerized
to the degree that if the test surface is in fact human skin, then changes to the outer skin
surface as a result of the occlusivity of the resin itself will not be manifest in the replica.
This replica that is produced directly from the surface of interest is called the "negative"
replica, "negative" because what ever goes "down" in reality, goes "up" in the replica, and
vice versa. For example, a whisker coming out of a man's beard goes "up" but in the replica,
it is manifest as a "hole" (e.g. goes "down").
The white powder for converting the negative to a positive replica (one that exactly replicates
the original surface) can be used to replicate the replica, thereby generating a high resolution
"positive" replica of the surface under study. Instructions for making the positive replicas
follow below. The positive replica has an indefinite shelf life, but the negative replica may
deteriorate with time, so conversion of the negative replicas to positive replicas should be
done within a few days following replication.
Making the negative replicas
The area to be replicated should be selected, ideally a circular area not more than 20 mm
(about 0.8 ") in diameter. If the surface need not be treated 100% non-destructively, then
using a SPI # 05022-AB Diamond Scribe, an arrow or some other fiduciary mark can be applied
next to the specific area of interest so that when later replicas are made from the same
identical area, these identical areas can be readily located in the SEM using such landmarks.
While the optimum cure time is dependent on the quantity of catalyst used, and also the
temperature, typically, several drops of catalyst in a volume of 5-10 ml of resin would
result in a cure time of roughly 20-30 seconds to partial completion (no changes in the
surface being replicated will be manifest in the replica) to about two to four minutes
until the replica is really cured (suitable for removal and storage for conversion to a
positive) . We like to wait for at least 5 minutes just to make sure that the replica is
not removed too soon; waiting longer will not harm the replica, although it may annoy live
subjects.
To obtain maximum working time in situations where the initial curing time is not of
importance, such as inert surfaces like shoes or painted metal, as little as one drop
of catalyst may be used, extending the curing time to several minutes. We recommend,
however, that no more than 10 ml of resin be prepared at one time because of the difficulty
of intimately mixing the two ingredients without incorporating air bubbles.
The best results are obtained by literally rubbing or massaging the curing system onto the
surface being replicated (both to ensure optimum mixing of the two ingredients and to reduce
the possibility of the presence of air bubbles) a second layer of resin is recommended in order
to give the entire negative replica more "body", which is needed to make the negative more
durable for the positive replica step.
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Tuesday December 02, 2008
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