HYACINTH. - See Zircon.
IDWALL STONE. - See Hone Slates, article 4.
IRON STONE. - A straight slab of the haematite iron ore, ground flat on the one face, is sometimes used by the Sheffield cutlers after the yellow German hone, in polishing the "cannell " or chamfers made by the German hone in setting razors. - The iron stone is very hard, and leaves a very smooth edge, almost fulfilling the purpose of the razor strop, but it must be used very lightly and sparingly. See the article on setting razors, Chap. XXXIII. Section 2.
JACINTH or Hyacinth. - See Zircon.
JADE is polished by lapidaries like Carnelian but it only takes a greasy and not a brilliant polish.
JAPANNED WORKS. - Such of the japanned works as are baked in ovens, for the evaporation of the solvent of the varnish, are 1st forwarded with pumice-stone powder applied with water on list or flannel; 2ndly they are polished either with rottenstone or putty powder and oil, also on flannel; and 3rdly with the dry hand and rottenstone.
JARGOON. - See Zircon.
The articles on Jet and Cannel Coal (vol 1, page 162 - 3) describe an entirely different method of working these peculiar substances, and to which the reader is referred. See also Cannel Coal in this Catalogue.
LAPIS LAZULI "is used in jewellery, but is chiefly important as affording that beautiful pigment ultra-marine, so highly valued by painters on account of its great advantage in not changing by time or exposure." - In producing this pigment the mineral is simply calcined and then levigated. The lapis lazuli is difficult to polish on account of the irregularity of its substance, which abounds in soft parts that wear away more quickly than the remainder; it is treated as Carnelian.
LAPS, metal polishing wheels, see Wheels, articles 37 to 47.
LAVAS, which are occasionally arranged as specimens, do not in general admit of being well polished, because of their being irregularly hard and soft, and also scoriacious; they are worked by the lapidary just like Alabaster, which see.