Keep chocolate at a good working temp., between 85°F and not exceeding 89°F by occasionally placing chocolate on bain marie to gently raise temperature for a minute or so.
Add the second portion of chocolate and stir until the temperature drops to 85°F (should take about 10-15 min.) Test the chocolate's temper-Dip one side of a small strip of parchment into the chocolate, then set aside to cool and harden. After about 5 minutes you'll be able to tell if the chocolate is properly tempered or if there is a grittiness or bloom (looks streaky).
Temper the chocolate. Weigh out a large portion of the chopped chocolate. Weigh out another portion which is 25% the weight of the first. Add larger amount to a pan in a bain marie and gently heat the chocolate until it reaches 120°F. Remove from heat.