Specification of Letters Patent No. 56,180, dated July 10, 1866

To all whom it may concern:

   Be it known that I, EDSON P. CLARK, of Northampton, in the county of Hampshire and State of Massachusetts, have invented a new and useful Improvement in Pencils for Producing Indelible Writing on Linen and other Fabrics; and I do hereby declare that the following, taken in connection with the drawings which accompany and form part of this specification, is a description of my invention sufficient to enable those skilled in the art to practice it.

   The nature of this invention consists in the employment of gypsum and black lead incorporated together, (and either with or without the addition of asphaltum or of lamp-black,) in connection with nitrate of silver, to be made into pencil-leads, which are inclosed in wood or other material for the purpose above stated.

   The ingredients used are nitrate of silver, gypsum, black lead, and asphaltum. The nitrate of silver is the indelible ingredient, as is also asphaltum, to some extent. The gypsum forms a hard compound, not readily softened by absorbing moisture from the air. The black lead is the immediate coloring-agent, (as is also the asphaltum or the lamp-black, if added,) giving instant color or shade to the writing before the oxidation, or blackening of the silver takes place by the action of light or heat, and the black lead and gypsum permit the pencil to be readily pointed.

   The mode of manufacturing these pencils preferred by me is as follows: The nitrate of silver is put into a heated porcelain crucible. When it is melted black lead is added in proportion of about one-eighth, and then calcined gypsum is added to this compound in proportion to the silver of one-fourth to one-half. The compound is then stirred with a spatula. A small quantity of lamp-black or asphaltum can then be added, according to the degree of blackness required in the mark of the lead. The quantity of these two last ingredients should be small, or they can be wholly omitted. A small quantity of this compound is taken from the crucible (which is kept moderately heated) by the spatula or knife, and placed upon the face of a die having grooves corresponding in form with the leads. The upper half of the die is then brought down with great force, and having similar grooves corresponding with the lower half, it forms perfectly round leads, the sudden compression hardening and cooling them. Each lead is then placed in a groove sawed in a cedar wood, and then covered with ground shellac. The whole is then placed in a gently­heated oven, when said cement melts and adheres to the lead and wood. A filler or strip of cedar is then placed in the groove and gently pressed down, sealing the lead in its place, rendering it impervious to air or moisture, and admitting of its being sharpened for use. These pencils are then polished, boxed, and labeled, being ready for use, and will keep any length of time. They are used like any ordinary lead-pencil. The linen to be marked is simply dampened in salaratus or soda water, or other like fluid, and the writing, after exposure to the sun a short time, becomes indelibly fixed in the fabric.

   The use of the gypsum with the nitrate of silver forms a lead not readily sensible to atmospheric influence, and the black lead imparts to the lead a capability of being drawn to a fine point, as well as of giving the immediate marking property to the instrument.

   This invention is an improvement upon the pencil patented by me May 3, 1859.

   I claim -

   The employment of the ingredients, in combination with the nitrate of silver, substantially as and for the purpose set forth.


      WM. H. ALLEN.