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Hi, I have issues with sealant / matte finish by quite some time now. It's not the dreaded frosty effect, what happens is to have a somewhat "dusty" result, as if the model is covered in dust.
This happens whatever the sealant I use (GW mostly, but also Army Painter). I've tried everything, shaking the can for more than usual, spraying by from a distance or nearer the model, in short sprays or longer ones...
One factor seems to be humidity level: on hot windy days it doesn't happens or happens very lightly. But I have tried dehumidifying the room via Aircon set to "dry" for about 20 minutes, but the dusty finish still appeared.
Also, very short streaks of spray seems to cause it more often than a longer spray.
I can't wrap my mind around this. In the hiscool years I used whatever at hand (GW, Armory, but also craft store sealants) without even considering the humidity level, and never had an issue with spray finish. What had changed by some years? It seems I'm unable to find a reliable manufacturer and a reliable method (I can't wait for the spase windy days to seal my minis). Now I fear the disaster each time a finish a model. Should I revert to use brush on sealant?

Yup.
So if you really cant prime on nice days then revert to brush or use an airbrush.
In this day and age people are cutting corners with manufacturing processes and cans can vary wildly.
With more units being sold who's to say yours wasn't at the end of the line or has been badly stored/transported.
The risks are just too high after the costs of the models and time involved.

From the sounds of it, you are doing this indoors as well?

and ditto with Alex.
its convenient not having to clean and set up the airbrush for varnishing but the fact that i dont have to fear the frost reaper is very nice.

Thanks for commenting!

@Alex: I don't think it's just an unfortunate can, as sealing has become tricky by quite some time now, and across multiple manufacturers...

@Desubot: I thought about getting an airbrush just for sealing minis... more so for this scope only, a cheap one should be enough.
I usually spray on the balcony (to avoid a family war) but I had same issue indoor (after running aricon set on "dry" in the room for over 20 minutes). To the other hand, the only models that didn't showed the dreaded dusty effect this month, has ben sprayed on the balcony (in a windy day, humidity at 52% - checked before spraying).

Point is that by now I get the "dusty" effect the majority of the times. Sometimes is barely noticeable, but I see it happened by the border of the bases (that I usually paint plain black) and on the metals (it totally kills shine). I suppose I'll go by brush and start looking for a unexpensive airbrush set...

Even though you say it's not the "frosty" effect, I'm guessing it's the same effect just less extreme, so the model looks dusty rather than completely frosted.

As to why it's happening? Well, lots of reasons are possible. Maybe you're applying layers too thick, maybe spraying from too far away, maybe your underlying paint is already quite matte.

Try applying very thin coats, waiting for it to dry before applying the next. Spraying from a closer distance, but also being careful to do thin coats (ie. move your hand quickly). You could try swapping to a satin rather than a matte. You could try applying a gloss first and then do multiple thin coats of matte to reach your desired level of sheen.

Do you have an airbrush? I always find airbrush varnishing far more reliable than either hairy brushing or spray cans.

Thanks for your reply.

AllSeeingSkink wrote:
maybe spraying from too far away,

So this can be an issue, right?
In my research I've found two main reasons for the dusty/frosted effect to appear:
1) humidity in the air that it's trapped between the model and the varnish
2) varnish that start to set before reaching the model
I don't know the reliability of these informations, but tha's what I have based my tests trying to avoid the problem. Up to today with scarce results...

AllSeeingSkink wrote:maybe your underlying paint is already quite matte.

So, even if spraying in dry weather, from the right distance and in thin coats, you're saying that applying too much varnish (too many coats) could generate the dust effect anyway?

 Gabbi wrote:
Thanks for your reply.

AllSeeingSkink wrote:
maybe spraying from too far away,

So this can be an issue, right?
In my research I've found two main reasons for the dusty/frosted effect to appear:
1) humidity in the air that it's trapped between the model and the varnish
2) varnish that start to set before reaching the model
I don't know the reliability of these informations, but tha's what I have based my tests trying to avoid the problem. Up to today with scarce results...

Spraying distance is a tricky one with matte varnish. If you're doing very light coats on an otherwise glossy model, you can get away spraying from a distance, if you're doing heavier coats or spraying something that is already matte, sometimes it can cause a dusty finish.

I will admit I don't know a whole lot about humidity.... I live in Melbourne, we don't get terribly humid here so it's not a problem I usually have to deal with.

AllSeeingSkink wrote:maybe your underlying paint is already quite matte.

So, even if spraying in dry weather, from the right distance and in thin coats, you're saying that applying too much varnish (too many coats) could generate the dust effect anyway?

Sometimes I've had that experience. The reason matte looks matte is because the surface has a microscopic rough grain to it, to me it seems like sometimes when you spray matte on top of matte on top of matte the latter layers pick up on the microscopic ridges of the previous layer. I've had models which looked dusty after applying too many layers of matte and you could feel they had a really rough texture which was actually quite delicate (you could gently scratch it and it'd leave an area with a more satin finish). I fixed it by hitting it with a satin coat to knock down the effect a bit.

I've had the most luck spraying the model gloss or satin (for the sake of protection) first and then doing very light layers of matte to knock back the shine until I'm happy. Otherwise using a satin varnish to begin with if you don't need the really flat look.

Sometimes I think people like the super-flat almost dusty look because it acts a bit like a filter, tying the different colours on the model together.

Thanks again. WIll make some more tests.
Anyway, I'll start looking for an entry-level airbrush

You certainly don't need an airbrush to get by, I just asked if you had one because varnishing is one of those tricky areas where it's easy to get poor results and airbrushing tends to be a bit more reliable. That said I get frosting airbrushing Vallejo's Acrylic Satin, so it's definitely not fool proof.

Hairy brushing matte varnish I sometimes get mixed results, some models I've hairy brush matte varnished came out fine others look a bit chalky.