Silvering may be caused by insufficient heat to fully melt the adhesive layer, but in digital imaging applications this problem is more likely to be caused by the excessive heat needed for a “high-melt” laminating film, or the heat built up when laminating too slowly. Ink jet output often needs to be laminated before it is fully dry, so heat can drive vapor out of the moisture in the ink. Use a “low-melt” laminating film. Keep the laminating speed up. One little known trick of the trade is to run the item image down (provided you are laminating 2 sides with the same film on top and bottom). This will get rid of that last bit of silvering which will typically show up on the dark areas of the image (where ink coverage is heaviest).
Silvering is often seen when laminating with cold films too. With many cold films, this silvering will go away by itself in a day or so as the adhesive penetrates and pushes the air through the back of the sheet. If silvering is extreme, the film may benefit from a heat assist. Cold laminating does not work well in a cold room, and most cold adhesives will flow better with a heat assist even in hot weather.