If the
ground glass cannot be had, a good substitute-also useful for a
camera glass-is plain glass with a sheet of tissue paper (or the
packing paper of films) stuck on with paraffin wax.
The dressing of objects to show up clearly is often needful. Incised
objects can be filled in with charcoal powder if light, or chalk if
dark; in any case a coarse powder, so as not to stain the object. For
faint cutting on glass or crystal go over the lines with 'China ink
in a pen, so as to cover them. Harden the ink in the sun, and then
gently wipe with a damp finger until all the excess is removed and
only the roughness of the lines remains black. On large objects light
dust or sand is often useful, to make relief clearer.
For objects in a bad light, or in the interior of tombs, reflected
light must be used. Lids of biscuit tins serve well; a lid in the sun
sixty feet off, and another lid reflecting the light on to a wall,
will suffice for a two minutes' exposure of a slow plate. Three or
four successive reflections into a totally dark chamber will suffice
in five or six minutes.
When an important subject cannot be revisited it is well to take
duplicates; the camera should be shifted laterally a few inches for a
near object, or a few feet for a distant view, and then the two films
will form a stereograph, if both succeed.
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