Fenton Wells asked:
"Looks like I was wrong and it is not mildew but an acid from the tube that it was stored in. It's brown. The freezer and drying it didn't budge it. Not sure it's worth going too much farther.
Anyone know a good source for Howard Fogg railroad prints?"
Time to step back and answer a few questions:
1. Is this a numbered and signed print? If it's a low numbered, signed print of a popular subject, it might be worth investigatigating restoration.
2. If it isn't numbered and signed, you might be able to get another copy at a reasonable price. Check eBay to get an idea of the market - a search on "Howard Fogg" returned 310 hits.