I’m just a hobbyist and these are my experiences…
There are many railroad modellers out there who are very good at finding substitutes for the more expensive hobby products. I’m not one of them. I’ve always been disappointed when cutting corners, so I just don’t do it.
But the one substitute I do use is Future as a gloss varnish. It is an acrylic floor wax that modellers have been using for a very, very long time. Scale aircraft modellers even dip canopy parts in it to enhance the clarity. Currently it is called Pledge Revive.
There has been much talk amongst scale modellers over the years about how the Future formula has changed. This came about when dipped canopies and glossed white models turned yellow with age. I’m not sure where that stands now, but since I don’t do either I think it is safe to use my railroad models.
I mainly use Future for decals but lately I have been applying it over top of color base coats on all brass model parts (and then flat coating on top of it later). My current thinking is that a gloss varnish is more durable than just a flat varnish on a base coat. Time will tell.
1. It can be brush applied as lots of modellers do, but I mainly airbrush it full strength (no thinning).
2. I have found that using an airbrush with a very small tip orifice does not make a good finish. It turns out pebbly, not at all smooth – at least this is my experience with spraying Future with my GREX XB (.30mm[.012”] tip). And thinning it a lot doesn’t help. The orifice diameter is too small. This is confirmed by others on various scale modeling forums.
I think that most modellers do not have a dual-action airbrush with a tip as small as .30mm, so this effect may not be well known. Most airbrushes have .50mm[.020”] opening which I think provides a better gloss finish. .50mm doesn’t sound like much of a difference, but the orifice cross-sectional area is 3 times bigger than .30mm.
I tried an inexpensive Badger 350 single action with the medium tip (.66mm[.026”] orifice) and the difference is dramatic. I get fairly smooth finishes with a 25 psi setting (full strength Future).
3. All glossing must go on wet, that is, it must be quite wet when it hits the model surface. I find that Future is very forgiving if a bit too much is applied, and it dries quite thin. But too much may cause runs. If too much hold this area horizontally until dry. Like many model railroad skills, it takes some practice.
4. For decals I apply two airbrush coats waiting about an hour in between.
5. For clean-up, I run 70% rubbing alcohol through the airbrush and then rinse it dismantled with warm water. Sometimes I give it a further cleaning (dismantled) with lacquer thinner.