See also:brush used in
See also:painting, and still employed to denote the finer camel's-hair and
See also:sable brushes used by artists, but now commonly signifying solid cones or rods of various materials used for writing and
See also:drawing . It has been asserted that a
See also:manuscript of
See also:Theophilus, attributed to the 13th century, shows signs of having been ruled with a black-lead pencil; but the first distinct allusion occurs in the
See also:treatise on fossils by
See also:Conrad Gesner of Zurich (1565), who describes an article for writing formed of
See also:wood and a piece of lead, or, as he believed, an artificial composition called by some stimmi anglicanum (
See also:English antimony) . The famous Borrowdale mine in
See also:Cumberland having been discovered about that
See also:time, it is probable that we have here the first allusion to that
See also:great find of
See also:graphite . While the supply of the Cumberland mine lasted, the material for English pencils consisted simply of the native graphite as taken from the mine . The pieces were sawn into thin sheets, which again were cut into the slender square rods forming the " lead " of the pencil . Strenuous efforts were made on the continent of
See also:Europe and in England to enable manufacturers to become
See also:independent of the product of the Cumberland mine . In
See also:Nuremberg, where the great pencil factory of the
See also:family (q.v.) was established in 176o, pencils were made from pulverized graphite cemented into solid blocks by means of gums, resins, glue,
See also:sulphur and other such substances, but none of these preparations yielded useful pencils . In the
See also:year 1795 N . J .
See also:Conte (q.v.), of
See also:Paris, devised the
See also:process by which now all black-lead pencils, and indeed pencils of all sorts, are manufactured . In 1843
See also:William Brockedon patented a process for compressing pure black-lead powder into solid compact blocks by which he was enabled to use the dust, fragments, and cuttings of fine Cumberland lead . Brockedon's process would have proved successful but the exhaustion of the Borrowdale supplies and the excellence of Conte's process rendered it more of scientific
See also:interest than of commercial value .
The pencil leads prepared by the Conte process consist of a mixture of graphite and
See also:clay . The graphite, having been pulverized and subjected to any necessary purifying processes, is " floated through a series of settling tanks, in each of which the comparatively heavy particles sink, and only the still finer particles are carried over . That which sinks in the last of the series is in a
See also:condition of extremely fine division, and is used for pencils of the highest quality . The clay, which must be
See also:free from sand and iron, is treated in the same manner . Clay and graphite so prepared are mixed together in varying proportions with
See also:water to a
See also:paste, passed repeatedly through a grinding
See also:mill, then placed in bags and squeezed in a
See also:press till they have the consistency of stiff dough, in which condition they are ready for forming pencil rods . For this purpose the plastic mass is placed in a strong upright cylinder, from which a plunger or
See also:piston, moved by a
See also:screw, forces it out through a perforated
See also:plate in a continuous
See also:thread . This thread is finally divided into suitable lengths, which are heated in a closed crucible for some
See also:hours . The two factors which determine the
See also:comparative hardness and blackness of pencils are the proportions of graphite and clay in the leads and the
See also:heat to which they are raised in the crucible . According as the proportion of graphite is greater and the heat
See also:lower the pencil is softer and of deeper black streak . The wood in which the leads are cased is pencil
See also:cedar from Juniperus virginiana for the best qualities, and
See also:pine for the cheaper ones . A
See also:board of the selected wood, having a thickness about equal to
See also:half the diameter of the finished pencil and as wide as four or six pencils, is passed through a machine which smooths the
See also:surface and cuts
See also:round or square grooves to receive the leads . The leads being placed in the grooves the board is covered with another similarly grooved board, and the two are fastened together with glue .
When dry they are taken to rapidly revolving cutters which remove the wood between the leads . The individual pencils thus formed only need to be finished by being dyed and varnished and stamped with name, grade, &c . Instead of wood,paper has been tried for the casings, rolled on in narrow strips which are torn off to expose fresh lead as the point becomes worn down by use . Black pencils of an inferior quality are made from the dust of graphite melted up with sulphur and run into moulds . Such, with a little
See also:tallow added to give them softness, are the pencils commonly used by carpenters . Coloured pencils consist of a mixture of clay, with appropriate
See also:mineral colouring
See also:wax, and tallow, treated by the Conte method, as in making lead pencils . In indelible and copying pencils the colouring matter is an aniline preparation mixed with clay and
See also:gum . The mixture not only makes a streak which adheres to the paper, but, when the writing is moistened with water, it dissolves and assumes the appearance and properties of an
See also:ink .
PENATES (from Lat. palms, eatables, food)
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