<prompt> Why do direct filling golds have to be flamed before insertion into the cavity preparation?To remove contaminantsTo make gold softTo form oxide layer on the surfaceAll of the above  <response>: Proper desorption is a matter of heating long enough at a temperature that removes contaminants and in the case of powdered gold, that burns away the wax.Ref:Phillips Science of Dental Materials ed 12 pg 414 