Up until recently I had most of my colour film processed and scanned to CD at a drugstore photo place. When I was developing film there, I often found that when I got my negatives back there was a sort of scaly effect in areas of images that had little variation in tone (mainly skies.) I know that the "scales" were on the negatives themselves because if I did my own colour enlargements of the image it was still visible. I thought the problem was that I was using some crappy cheap and expired film for snapping photos when I was out and about, but when I shot a roll of fresh Ektar 100 and brought it too the same photo place, I still got some scaly photos back (not as much though, which i attributed to the finer grain of the Ektar.)
Since then I've started taking my colour film to another place to be processed, however it's more expensive and the CD of scans isn't included in the price of development, but I have seen absolutely no scales on my images. I am wondering if this effect is caused by old or bad chemicals that they might not have bothered to change at the drugstore? and if the only solution to preventing this is by going to a more professional place.
I've attached an image of what the effect looks like.