Remember the VW rat Jesse James built on Monster Garage? It had a glass front end and somehow they made it as rusty as the rest of the car. I think they put ground up metal shavings in clear and painted that on the car.
Regular Vinegar works just as well as their "special" acid.
To get the best colors,keep the surface wet as long as possible.
I cover the surface is plastic,you can also soak cloths in acid
to keep the surface wet longer.
If the acid evaporates too fast,you get that cheap looking
Orange "flash rust",not the right warm tones.
You can also just apply the paint,and let it rust naturally.
Michael's carries it,watch for the 40 or 50% off coupon in their weekly flier.
WOW!
That is interesting- I do have to say it looks fairly convincing.
This year at Back To The 50's a group of about 6 of us were checking out a
very vintage "barn find" '32 Ford coupe. We probably looked at it 2-3 minutes before someone read the description sheet taped to the window in which it said "new fiberglass body". We were all shocked.
The car even had fake bird droppings on the front of it!
It is impressive what some skilled painters can pull of nowadays!