Hi;
What I have discovered is this. NMF in paint is not the ideal maskable surface. I have not had that much luck with any of the paint brands discussed and Masking NMF. Now when I do Bare Metal Foil. then I get it done beautifully. What I do is this When finished with the foiling I start handling the model with White Cotton Museum Gloves.
I then take De-Natured Alcohol and put some on a clean soft remnant of an old " T " shirt.( No dust fuzz that way) I let it almost dry then gently rub it all over the model. This removes my oils from handling it and Most importantly, removes the microscopic traces of release oil from the machinery used to make the foil! The Decals should be installed at this time too. They will stick better!
I then use Draftsmans tape, well burnished at the edges to mask the foil finish. I spray at low pressure and remove the Tape as soon as the painting is over. This lets the paint at the edges settle down instead of making an edge. Believe it or not, You can also use Scotch Magic Mending tape for this. You must first run the tape through your fingers to lessen the stick. It does work , but you have to concentrate on what you are doing!
Yes! The BMF is labor intensive. But what I like is when you are done, just before you say finished. You gently buff the model, again with a fuzz free cloth, I have use cloths for cleaning Eye-Glasses. Remember, I said gently,You now have decals on there! Then Clear - Coat it in Gloss or Semi-Gloss, let dry in a dust free environment for at least two full days and Vio'la, A beautiful NMF model!
There are instances where I do not overcoat the model with clear. As in Model rail Passenger cars of the Santa Fe and Amtrak older cars. Why? Well, I noticed that when I leave them coating free they buff up regularly to like new brightness. You cannot do that with an overcoat of paint. Paint, No matter whose it is, WILL, yellow over time. It's the Nature of the beast.