opera glaze is used on opera tortes(3 layers of yellow chiffon w/ 2 layers of coffee buttercream and 1 layer of ganache in between the cakes and then covered with the glaze) it consists of coating chocolate, dark couverture chocolate and vegetable oil. To make the glaze: melt both chocolates together over double boiler, once melted stir in the oil, the glaze makes a thin coating on the cake that sets up solid. You want to let the opera glaze cool slightly before using it.
Sacher glaze is used on sacher torte (2 layers of sacher cake, apricot jam filling, covered with ganache, and then covered with sacher glaze) this glaze consists of heavy cream, dark couverture chocolate and butter. The added fat in this glaze allows the coating to set up firm but not solid and have more of a ganache flavor. To make this just bring heavy cream to a boil pour over chocolate in a bowl, wait a few seconds before whipping together, whip together, then add in butter until melted. This glazed should be used as soon as possible.
the recipes for both are as follows:
for about 12 oz of opera glaze
coating chocolate 8 oz
dark chocolate couveture 3.5 oz
veg oil 1.33 oz
or if you can't be bother getting 2 different types of chocolate you can use all couveture just increase the amount of oil i've done both and they come out exactly the same:
dark chocolate couverture 11.5 oz
veg oil 2 oz
for about 14 oz of sacher glaze:
heavy cream 6 oz
dark chocolate couverture 6 oz
butter 2 oz
i hope this helps let me know how the cake comes out :)