glace (de viande) and demi-glace two French culinary terms which are less closely connected than might be supposed but which can conveniently be treated together.
Glace de viande is meat glaze, a greatly reduced meat stock which has a syrupy consistency and can be used to impart its flavour and a shiny surface to appropriate savoury dishes, and to give additional flavour and body to sauces. References to this meat glaze at the beginning of the 19th century include Viard (1806), who describes how a veal stock which has been reduced to the consistency of a sauce can be used as a seasoning, and Beauvilliers (1814), who uses a little brush of chicken feathers to brush his meat glaze (glace, ou consommé réduit) over foods which will benefit from a ‘glazed’ appearance. Meat glazes are now rarely used, since their preparation is expensive and arduous.