Acrylic matt varnish - looks like frost!

[Vicw]

I have recently built an Airfix 1/72 hurricane Mk1. I brush painted it with Humbrol Matt enamal paints. Before applying the decals I sprayed the model with Humbrol enamal gloss from an aerosol can to form a smooth surface. After applying the decals I again sprayed it over with Humbrol enamal gloss from the aerosol can to "seal" the decals. At this point I decided to change the surface finish from gloss to matt to make it more in keeping with the real thing. Rightly or wrongly I used acrylic Matt varnish from the Humbrol Acrylic Matt Colours range, in fact number 49 in the 14ml pot size. I decided to airbrush it which of course meant thinning it. I used ordinary tap water to thin it but the water was taken from a charcoal filter tap even though the charcoal filter itself hadn't been changed for months. The varnish seemed to airbrush on to the model with no problem but after it dried the finish was very poor. I can only describe it as looking like the model had been kept outside on a very frosty night. The finish just looked milky in colour. Prior to stirring the varnish in preparation for airbrushing I noted the varnish itself appeared to be a milky colour rather than clear. 

i would really appreciate any advice from other modellers who have experienced the same problem and what they did to fix it. 

[Dave Leeman]

Hey Vicw, I had the same thing happen, although my acrylic matt varnish was from a Humbrol rattle can, and yes, it does look like hoar frost, I assumed it was a reaction to previously applied Johnsons Klear, but after experimenting with differing finishes of acrylic and enamel the frost effect appeared everytime?

 

 . . . Dave Leeman

[Frederick Kullas]

The white is the matting medium. There is too much of it. Thin the varnish and put it on in very thin coats. Not much can be done when it comesfrom a spray can though.

A fix which often works is to use a thin coat of gloss varnish over the white. The gloss varnish soaks it up. With acrylic varnish which has dried lightly brush over the area with an alcohol such as meths, to soften the layer of matt varnish, then apply the gloss varnish. Do not use too much alcohol though as it may start to affect the main coloured paint layer.

I use acrylic 49 matt varnish, and I thin it so much that I end up with two plastic pots filled to the brim, any less thinning and I get the occasional white too.

 

hth

[Vicw]

Thanks to you both (Dave and FredErick). I know what to do if it happens again. A few days have passed since I had the problem, enough to regain some confidence. I rummaged around in my paints box(s) and found a half full Humbrol matt aerosol spray can and gave it a couple of coats. That seemed to pretty much completely cover over the White (matting medium). When I originally airbrushed the model with the plastic pot of 49 I thought I had thinned it enough, enough anyway to get it freely through the brush nozzle (0.3mm). I guess the viscosity looked like full fat milk, so I was happy with that. I didn't give a second thought to Fredericks point about thinning even further to dilute the matting agent more. I'll look out for that next time, and also the point about using thin layers. I had the air pressure set at about 20psI and noticed rather a lot of varnish almost pooling if I left the brush too long in the same place.