GB575867A - Improvements in coloured marking leads or elements - Google Patents

Abstract

575,867. Pencils; ink. FERST, Ltd., M. A. April 19, 1944, No. 7202. Convention date, May 1, 1943. [Class 146 (iii)] A colour marking element or pencil for making marks similar to those produced by crayons, or indelible pencils is formed of a mixture containing clay and a material which when fixed is softer than clay so as to produce in the fired clay portion masses of softer material. The material may be made by mixing water with 5 per cent to 70 per cent by weight of clay, and 95 per cent to 30 per cent of a non-plastic hydrated silicate, and then adding to the mixture 20 per cent to 70 per cent by weight of the total mixture of a finely divided material which can be subsequently wholly or partly removed, such as carbon black which can be removed by oxidating naphthalene by volatilization, or finely divided copper or copper oxide removable by acid treatment. The silicates used may be talc, pyrophyllite, or mica, raw or calcined. The materials may be proportioned so as to vary the porosity of the material, and also its hardness. The material is finally treated with an impregnant which is chosen so as to produce an insoluble or soluble written mark. Various impregnants may be used, and include water soluble waxy materials, wax soluble colouring material, water soluble colouring materials, or combinations of these. The impregnant is preferably fluid at some temperature above 154‹ F.