at once comes to the fore. I have, however, known of instances where the
picture needed no toning.


OPAL PRODUCTION IN PRACTICE.

This is still a secret with some in the profession. A limited number
of workers have succeeded in bringing out good opals, and their _modus
operandi_ is kept from the many. Now this is a pity, when one considers
the great charm attached to a good picture on opal, with pure whites and
rich blacks, and in many localities the demand that might be created for
them. Apart from their beauty, another charm attaches to opals--their
absolute permanence; and this, it must be allowed, is no trifle. What,
in fact, can be more painful to the worker who values his work, and sets
store by it, than to feel it must ere long fade and pass into oblivion!
A properly executed opal will no more fade than the glass pictures so
common at one time, and which, wherever taken care of, are as perfect
now as they were when first taken.

Now, excellent pictures are to be made on opals by means of emulsion;
but I propose first taking the transfer method (mainly applicable to
ground opal and canvas) as given above for pottery, since in practice
it is found very ready, easy of manipulation, and safe. The details are
much the same as above, and necessitate double transfer.

After the picture had been obtained on the plate (ordinary glass plate),
and after thoroughly fixing, washing, and toning, the picture (and this,
remember, is the case likewise with terra-cotta) then has to be loosened
from its support, and this is done with a solution of sulphuric
acid--one drachm to fifteen ounces of water--which is made to flow