Here is what camera operator Len Harris, in our BRIDES OF DRACULA issue #14, had to say about that scene:
"...the scene where Peter Cushing burns out the vampire's bite was well done. We started with a long shot of Peter pumping up the fire.He put a real poker into the fire and stirred up the real sparks. We tracked into a close-up for a reaction from him. While Peter's arm was moving as if stirring the fire, he dropped the real poker and picked up the wooden one from the property man. The prop man moves back and so does the camera. Peter holds up the prop toward the camera to show that it is "hot" (a special effects trick) and then puts the prop on his neck and reacts as you would expect the character to. The strength in the shot is Peter Cushing's acting, because when he puts the poker on his neck, you really feel it."

Doesn't really say HOW the look was achieved, but certainly the scene works because of Cushing. By the way, we haven't done our print-on-demand reprints of back issues, like this #14, but it should be soon (family, etc, held it up) and one can read what I think is the ultimate coverage of what is my favorite Hammer film!