WATER-MARKING 235
is always placed after the first or second suction box, so that the amount of
water left in the web when it reaches the roll may be regulated.
It is in the careful and skilful manipulation of the water in the web when
the dandy roll touches it that the best results may be obtained, for if the web
is sucked too dry, no mark will show, and if left too wet it will be crushed
and 'worms' or 'tears' will appear in the sheet
The dandy roll performs two distinct functions. First, it closes up the
sheet, compressing the fibres together and generally improving the appearance
or look-through of the paper, and for this purpose it is not necessary to have
any design upon the roll; and, second, it is used for putting a name or device
into the paper. In a plain 'wove* roll the skeleton drum is covered with fine
wire cloth similar to the machine wire, and this roll does not actually water-
mark the paper, but simply closes it up. Very high speeds may be attained
on 'news' machines, using a plain wove dandy, provided the roll is of sufficient
diameter and of correct weight and construction.
A different type of roll, and one used chiefly on ledger and thick writing
papers, is known as a laid roll (Fig. 93, p. 228). This roll, instead of being
covered with wire cloth, is covered with a collection of thick brass wires bound
together at intervals of an inch or so by fine wires. Various gauges of wire
are used, and thus the number of wires to the inch may be varied to suit the
thickness or other characteristics of the paper. The thicker and stronger the
paper, the coarser the wire used and the fewer the number of wires to the inch.
Azure or blue papers look better with fewer wires to the incE than cream
papers. A medium substance of ledger paper usually has about 18 wires
to the inch, a writing paper about 20 wires and a thick, strong ledger about
16 wires.
Water-marking by means of a dandy roll is done by fixing a device or
letters worked in wire on the cover of the roll, and this may be done on either
a wove or a laid roll. The device stands out from the surface of the roll,
and the weight of the roll presses the wires into the soft wet web, forcing the
fibres away in all dirertbns and thus forming a thin place in the web. When
paper marked in this way is held up to the light, the device shows up as a
translucent pattern.
Formerly, water-marks served as trademarks for mills making the paper,
and to a certain extent this still holds good, although probably the greater
number of registered water-marks nowadays belongs to^he wholesale stationers
and printers. Some well-known devices are shown in Fig. 96. The marks
vary from simple words of a few letters to the most elaborate and artistic
designs—coats of arms, ships at sea, etc. Some very fine water-marking
is done on papen for postage stamps and bank-notes, and, generally