Andrew I would suggest that the embossing powder that you have do three or four stampted out images on scrap its of paper and experiment with your heat gun ie 1. heat and as soon as it changes move the heat gun it you do not like that then 2. keep it a second longer then move heat gun, and so on you get the feel of the embossing powder you are using. Hope this makes sense if not let me know and I will try and make my self clearer

Lorraine