Never melt chocolate over direct heat. The flavour will be impaired and it will ‘seize’ - go hard and grainy - if it becomes too hot.
Butter or oil can safely be added to chocolate before or after it is melted without any risk.
Chocolate can be added to a large quantity of hot liquid without any risk.
Chocolate can also be safely melted with a small quantity of liquid. If you add a small amount of liquid to melted chocolate, however, the chocolate will seize. If this should happen you may be able to retrieve it by adding a little oil.
Chocolate melts more evenly and quickly if it is broken or cut into small pieces. It should never be heated to a temperature greater than 44°C/110°F.