Class A.

"_Sizing._ Not more than 2 per cent. rosin, and finished with the
normal acidity of pure alum.

"_Loading._ Not more than 10 per cent. total mineral matter (ash).

"With regard to written documents, it must be evident that the proper
materials are those of Class A, and that the paper should be pure,
and sized with gelatine, and not with rosin. All imitations of
high-class writing papers, which are, in fact, merely disguised
printing papers, should be carefully avoided."

PASTES

To make paste for covering books, &c., take 2 oz. of flour, and 1/4
oz. of powdered alum, and well mix with enough water to form a thin
paste, taking care to break up any lumps. Add a pint of cold water,
and heat gently in an enamelled saucepan. As it becomes warm, it
should be stirred from time to time, and when it begins to boil it
should be continually stirred for about five minutes. It should then
form a thick paste that can be thinned with warm water. Of course any
quantity can be made if the proportions are the same.

Paste for use is best kept in a wooden trough, called a "paste tub."
The paste tub will need to be cleaned out from time to time, and all
fragments of dry paste removed. This can easily be done if it is left,
overnight, filled with water. Before using, the paste should be well
beaten up with a flat stick.

For pasting paper, it should have about the consistency and smoothness
of cream; for leather, it can be thicker. For very thick leather a
little thin glue may be added. Paste made with alum will keep about a
fortnight, but can be kept longer by the addition of corrosive
sublimate in the proportion of one part of corrosive sublimate to a
thousand parts of paste. Corrosive sublimate, being a deadly poison,
will prevent the attack of bookworms or other insects, but for the
same reason must only be used by responsible people, and paste in
which it is used must be kept out of the way of domestic animals.

Several makes of excellent prepared paste can be bought in London.
These pastes are as cheap as can be made, and keep good a long time.

Paste that has become sour should never be used, as there is danger
that the products of its acid fermentation may injure the leather.

Paste tubs as sold often have an iron bar across them to wipe the
brush on. This should be removed, and replaced by a piece of twisted
cord. Paste brushes should be bound with string or zinc; copper or
ir