........refers to applying a filter over three layers of gloss coat which is over the base coat.......
huh? .............that ain't right. You don't get a filter effect over a gloss coat. Don't matter how many.
What is a filter?
Diluted wash. 5% paint 95% mineral spirits or turpenoid over a flat finish. It can also be done with water and acrylic paint plus a drop of dishwashing liquid to prevent puddling / relieve surface tension, although I don't think it works as well.
I thought it was a wash?
A wash is like 20% paint and 80% thinner. It is applied over a gloss finish. It can also be done with water and acrylic paint plus a drop of dishwashing liquid to prevent puddling / relieve surface tension.
What medium is it?
The opposite of your last medium.
If it's acrylic based how do you keep it from ruining the acrylic paint job?
A good 24 hrs or more (is better) drying time for the paint. Same for the future. Never use alcohol over acrylics unless you really know what you're doing.
Do the gloss coats protect the base coat from the filter?
Yes, but because they are gloss, the effect will be a diluted wash. It has to be a flat finish to get the filter effect.
If the gloss coat is acrylic how do keep from ruining it?
Use oil based mediums.
If it's oil based how do you seal it from the oils washes?
Future. A semi or flat finish is the best for filters. For a flat finish seal it with dullcote and give it 24 before the filtering.
There is just "so" much that can be said. Follow the armor builds. The only real way you're gonna get this down is to hold your breath (and a cheap kit) and jump in with your boots on.
I hope maybe this will help you get on your way.