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Great Britain Patent 383,330
“An Improved Process for the Production of Writing and Drawing Leads”, 1930–1932

date of application
date granted
inventor
assignee
patent holder country
1931 August 20, No. 23,504/31; (1930 December 8 in Germany)
1932 November 17
Karl Kreutzer, Germany
J. S. Staedtler
Germany
patent employed on J.S. Staedtler Mars Lumograph
J.S. Staedtler Mars Lumograph drawing pencil

Leadholder Commentary

The essence of this claim is the substitution of pigmented oils/fats/waxes in place of un-pigmented ones in the lead making process. This makes the pencil markings more opaque and so can be reproduced with the light/shadow-based reproduction technology such as ozalid and blueprinting.

Pencil lead is typically made like this:

  • Powdered graphite and clay powder are mixed, water added, and kneaded into a “dough.”
  • This soft mixture is extruded into thin rods and cut to length.
  • These rods are fired in a kiln and vitrified just as any ceramic object would be.
  • When cooled, the leads are imbibed with oils and/or waxes to make drawing smoother. Every manufacturer has their own secret recipe for this component of the lead.

We, the firm J. S. Staedtler, (personally responsible partners: Rudolf Kreutzer, Walter Kreutzer, and Karl Kreutzer), of Rückertstrasse 9, Nürnberg, Germany, a Kommanditgesellschaft, organized under the laws of Germany, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement :—

This invention relates to the production of graphite writing and drawing leads adapted for preparing documents and drawings intended to be directly reproduced by means of light prints.

Ordinary pencil leads, copying leads and coloured leads, which are saturated with fatty material such as tallow, stearin, wax and the like, for the purpose of improving their writing capability, are ill-suited for the said purpose since the fat addition, which amounts to a considerable proportion of the lead, increases the light transparency of the marks produced with the lead. Obviously, for the object in view it is highly desirable that the marks be as opaque to light as possible.

This object is attained by the leads made in accordance with the present invention, which consists in incorporating with a graphite lead composition a fatty material containing fat-soluble light-absorbing colouring matter. Colouring matter made similarly to that usual in the production of carbon paper, for example, may be used.

The following specific example is given to illustrate one method of carrying out the invention: it must be distinctly understood, however, that the invention is in no way limited to this specific example. Pencil leads are made in the known manner from graphite and clay in the known proportions; for example 70% of ground crystallised graphite are mixed with 30% of clay, suspension, the mass dehydrated, mixed in kneading machines and then pressed into lengths. After drying the leads are ignited at about 1100° C. and saturated with a coloured fatty composition, so that the pores are completely filled with this mass. The fatty composition may, for example, consist of the following ingredients:

4 parts of Sudan yellow GG
4 parts of Sudan brown RRN
0.3 parts of Sudan black RT
100 parts of stearin.

The dyestuffs (which are made by the I. G. Farbenindustrie A.G.) are stirred into the fused stearin. The saturation of the leads is effected by laying them in the coloured fused stearin composition and leaving them therein for about 1 hour.

The present invention provides a lead which gives a mark of substantially improved light opacity and which, therefore, is preeminently adapted for preparing on tracing paper designs etc. which are to be reproduced directly in the form of light prints. Designs and the like prepared with the aid of these pencils yield copies which are very sharp.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:—

1. A process for producing graphite writing and drawing leads adapted for preparing documents and drawings intended to be directly reproduced by means of light prints, consisting in incorporating with a graphite lead composition a fatty material containing fat-soluble light-absorbing colouring matter.

2. The improved process for producing graphite writing and drawing leads adapted for preparing documents and drawings intended to be directly reproduced by means of light prints substantially as hereinbefore described.

3. Graphite writing and drawing leads whenever made by the process hereinbefore described and claimed.

Dated this 6th day of July, 1931. Marks & Clerk. —

Redhill: Printed for His Majesty’s Stationery Office, by Love & Malcomson, Ltd.—1932.