340
10.
PARTICULATE SPECIMENS
surfaces which can be dried, such as skin, do not present difficulty. There
have been many botanical applications of the method.
10.8. Preparation of Surfaces for Replication
Surfaces to be replicated are apt to require some preliminary preparation. If one is interested in mineral patterns as, for instance, in bone or
tooth, mild etching with weak acids may reveal detail not otherwise
visible, or freshly cleaved fractures uncontaminated by handling may be
the surfaces of choice. Metallurgists frequently begin with a polished
surface which is then etched. Surfaces like skin or hair should be degreased
using suitable organic solvents (Fig. 41). Paint and wood surfaces have
been studied after differentially extracting various components.
If a primary replica is to be made by a plastic such as Formvar dissolved
in an organic solvent, it is important that the solution wet the surface
completely and not trap bubbles. Ordinarily the specimen should be wet
with pure solvent first before flowing on the solution. If a very volatile
solvent such as chloroform is being used, care must be taken to avoid the
condensation of water droplets.
If a primary replica is to be made by the vacuum evaporation of carbon,
or some other substance, the surface of the specimen must be extremely
clean. The use of organic solvents as cleaning agents may be necessary,
but is particularly hazardous since trace quantities of nonvolatile impurities can so easily leave contaminating films that will leave their mark
on the replica, and quite likely bury the detail one seeks.
10.9. Materials for Replication, Deposited from
Solution or Melt
Surfaces can be replicated excellently by a variety of substances
deposited from solutions including particularly plastics and resins. In this
category, solutions of Formvar in chloroform or ethylene dichloride have
been most commonly used. Parlodion in amyl acetate behaves similarly.
Thin films, suitable as single-stage replicas, can be formed by flowing
dilute (approx. 1%) solutions of these substances over the surface to be
replicated, draining and drying. Thick films, suitable as the first replica
in two-stage replication, are formed if viscous, concentrated solutions are
used. It is also possible to thicken the replica by building up successive
layers of plastic.
10.
PARTICULATE SPECIMENS
surfaces which can be dried, such as skin, do not present difficulty. There
have been many botanical applications of the method.
10.8. Preparation of Surfaces for Replication
Surfaces to be replicated are apt to require some preliminary preparation. If one is interested in mineral patterns as, for instance, in bone or
tooth, mild etching with weak acids may reveal detail not otherwise
visible, or freshly cleaved fractures uncontaminated by handling may be
the surfaces of choice. Metallurgists frequently begin with a polished
surface which is then etched. Surfaces like skin or hair should be degreased
using suitable organic solvents (Fig. 41). Paint and wood surfaces have
been studied after differentially extracting various components.
If a primary replica is to be made by a plastic such as Formvar dissolved
in an organic solvent, it is important that the solution wet the surface
completely and not trap bubbles. Ordinarily the specimen should be wet
with pure solvent first before flowing on the solution. If a very volatile
solvent such as chloroform is being used, care must be taken to avoid the
condensation of water droplets.
If a primary replica is to be made by the vacuum evaporation of carbon,
or some other substance, the surface of the specimen must be extremely
clean. The use of organic solvents as cleaning agents may be necessary,
but is particularly hazardous since trace quantities of nonvolatile impurities can so easily leave contaminating films that will leave their mark
on the replica, and quite likely bury the detail one seeks.
10.9. Materials for Replication, Deposited from
Solution or Melt
Surfaces can be replicated excellently by a variety of substances
deposited from solutions including particularly plastics and resins. In this
category, solutions of Formvar in chloroform or ethylene dichloride have
been most commonly used. Parlodion in amyl acetate behaves similarly.
Thin films, suitable as single-stage replicas, can be formed by flowing
dilute (approx. 1%) solutions of these substances over the surface to be
replicated, draining and drying. Thick films, suitable as the first replica
in two-stage replication, are formed if viscous, concentrated solutions are
used. It is also possible to thicken the replica by building up successive
layers of plastic.