This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
Work to be brazed needs to be supported on a bed of some refractory material. Often a fire-brick or piece of fire-lump is used for heavy work, or powdered pumice or charcoal for lighter work. A fire-brick forms a convenient basis, and may be hollowed out to receive a dough-like compound of 1 part fine fire-clay and 2 parts charcoal dust combined by adding a little stiff rice-flour paste, as Edwinson suggests. Or pumice may replace the fire-clay. In this dough the article is embedded, and all is dried gently before the brazing begins. Freeman has introduced a new and improved heat deflector, for use with the blowpipe, as a support for the Work whilst it is being brazed or soldered. This article is made of a very light porous clay, specially prepared, and is corrugated, so as to allow the heat to pass entirely underneath the article to be soldered. It is superior as a support to that of an ordinary fire-brick, it does not burn like composition supports, it does not crackle or spit like charcoal, nor crumble away like pumice. The article has been tested by many of the leading electroplate and jewellery manufacturers of Birmingham, who speak highly in their testimonials of its efficiency.
Blocks of the material may be had in disc form 14 in. in diameter, or in lumps 12 1/2 in. square at3s. each.