It is usually necessary to do the final cleaning and preparation of
fossils at home or in the laboratory, for most fossils brought in from
the field require considerable preparation before they are ready for
display.
Excess matrix should be carefully removed with hammer and chisel; blows
should always be directed away from the fossil. Smaller tools (needles,
tweezers, and awls) should be used in the final preparation stage, and
one should work carefully to avoid damaging the specimen. Before
starting the final cleaning, it will be helpful to place the fossils in
water and let them soak overnight. This will loosen much of the excess
rock, and most of the softer material can then be removed with a small
scrub brush or tooth brush. Mounted needles can be used to clean more
delicate specimens or around the smaller structures of larger fossils.
It may be advisable to use the magnifying glass when working with small
fossils or with delicate surface structures of larger specimens.
Broken fossils can be repaired with clear plastic household cement, and
specimens that are crumbling may be coated with pure white shellac,
thinned collodion, or clear nail polish. The latter is preferred as it
is not as likely to crack. Fragments of bone are particularly apt to
crumble upon exposure to the air. This type of fossil is normally quite
fragile and should be excavated with great care and shellaced as soon as
dry.
Dilute hydrochloric acid may be used in removing silicified fossils from
a calcareous matrix. The material to be etched should be placed in a
pottery or glass container and covered with water. Acid should then be
added to the water very slowly and until large numbers of bubbles are
given off. Each time the bubbling ceases, more acid should be added and
this process should be repeated until the fossil is free of matrix. This
procedure should be carried on in a well-ventilated place, and the acid
should be handled with extreme caution. Hydrochloric acid can cause
damage or serious injury and the fumes are extremely corrosive.