It's called mottle. And the reason signmakers are still having problems is because it takes even longer to disappear when the weather is cooler. Why does it happen?

It happens because mottle, dull and flat-looking areas on high performance film, is a characteristic of conformability. The better the grade of high performance vinyl, then the more prone it is to mottle. Mottle can occur when vinyl is tightly wound. If left rolled this way long enough or heated for a while, the normally glossy surface takes on the impression of the backing or liner paper. Just as when high performance vinyl is installed against a rough surface, the same thing happens when it's pressed against the back of the liner long enough. It shows every imperfection.

By the way, the higher the gloss of the vinyl, the more you'll notice those dull spots. And color is also a factor. Dull areas are more distinct on darker colors than bright or light ones.

What can you do to fix it? First, prevent mottle from occurring on the rolls you already have in stock. For instance, when you store vinyl, loosen the roll slightly. Don't lay the roll on its side or you'll get those flat spots. Instead, use the same box it came in, which is specially designed to suspend the roll. Or, hang the vinyl from its core on pegs or special racks taking care to keep the rolls away from a bright window or direct heat source.

Secondly, if you ever do develop mottle, use a heat gun or hair dryer to gently and carefully warm the surface. You'll reclaim the gloss as well as the color. In warmer weather (90 degrees +), just unroll the vinyl. It may take an hour or so to disappear but you'll need to help the process along in the winter. Premasking the vinyl helps but this process can take days to remove the condition. Just remember that time alone removes mottle. After installation, you'll find that after a few days, the dull areas you so fretted over have disappeared!

So if your vinyl is looking a little dull and flat, rest assured that mottle is a really just characteristic of glossy, high performance films' conformability. Take steps to prevent the condition but learn how to tackle the problem when it occurs.