Humbrol Spray Failures

[sequoiaranger]

In the early '60's my mom and I traveled from my home in Southern California to London to visit my mom's brother working as Naval Attache to the US Embassy. I was truly STUNNED by the plethora of models in the LHS in the small town of Northwood (Airfix bagged kits @ $.28 USD a piece!!). I also picked up many Humbrol paint tins in all those "authentic" colors that Pactra and Testors back home couldn't hope to match. I loved the different smell, and the good coverage when using brushes (as I did on all my models back then--airbrushing would come in the 1980's). I bought lots of Humbrol thinner, too, as it seemed to work better with Humbrol paints.

In my past airbrushing era, I remembered the Humbrol paints as more difficult to airbrush, but as my current model (first in 15 years!!) was a British subject, I opted to honor my modeling heritage with Humbrol colors. "Matt 23" was a "Sky" white-green to which I added a little green and blue to get the "perfect" underside color. I thinned it with the Humbrol thinner and began to airbrush (also for the first time in 15 years, with a new compressor) the underside of my Avro Avatar. It worked fine. I put on another coat. It worked fine.

I turned the model over and put on the top colors (Testors/Pactra mix), but needed to touch-up the color break line along the bottom of the fuselage. THIS TIME, the Humbrol paint came out like cottage cheese, spattering or simply clogging the nozzel, then to gush out suddenly. Luckily I was using a "painting dummy" to try out first, otherwise I would have had a messed-up subject. I strained the paint through a micro-fine mesh funnel and got out the globs. This was a messy, time-consuming job. I had to wait a few days before painting again, but was "ready" to finish off my "Sky" paint and move on. Even with the micro-screening, the "new, improved" Humbrol paint was cheese yet again. I put more thinner in. No effect.

Dismayed, I tried to match/mix some Testors/Pactra paint to a similar color to finish off the model (will probably need to re-paint the ENTIRE underside  ).

Wuzzup with Humbrol? My other paints worked in the airbrush fine, and even the first (first TWO, actually) coats of the underside color came out fine. Why suddenly (with no other air pressure, nozzle settings, or thinning changes) did the paint glob and clog?? I am really perplexed, dismayed and angry (this setback may mean I cannot finish my model in time for my next IPMS monthly meeting!!).

Anyone else have such problems with Humbrol paints?? Am I doing something terribly wrong?

[Hobbes]

This happened to me as well recently, in my case I'd used too little thinner. A 1:1 ratio solved the problem. If you add thinner to the mix in the airbrush (instead of cleaning the airbrush and starting all over again), remember that the tube and channels inside the airbrush are still clogged with too-thick paint.

[sequoiaranger]

>in my case I'd used too little thinner. A 1:1 ratio solved the problem.<

WOW! Never heard of 1:1 in ANY paint.  I usually use about 2:1. I added some thinner to my faulty mix, and still it seemed that the paint balled up in clots surrounded by semi-clear liquid. I couldn't get a homogeneous mixture.

When I overcome my disgust, I may try that sometime, but for now, I think I need (psychologically) to get on with the model and futz with the Humbrol paints some other time!

Thanks for the hint; I will definitely try it!

[Weaver]

Just a mad thought - you are sure you've got Humbrol ENAMEL (in little tins) and not Humbrol ACRYLIC (in little plastic pots), arn't you? I'd imagine that acrylic paint in enamel thinners might react the way you've described; never tried it and not about to though!

Other than that, have you cleaned the airbrush with anything nasty that might have got into the paint mix?

[sequoiaranger]

>Just a mad thought - you are sure you've got Humbrol ENAMEL (in little tins) and not Humbrol ACRYLIC (in little plastic pots), arn't you?<

Yes, I'm sure. For one thing, the paints and thinners were acquired BEFORE there was such a thing as acrylic paints!! THAT might be the problem (age), though I have had many other paints "come alive" after decades of dormancy with no problems at all.

As far as a "mad thought", you know there is a "definition" of crazy that says a person is crazy when they do the same thing over and over again expecting different results. Here I was doing the same thing over and over again expecting the SAME results but getting different ones. I guess that proves *I'm* not crazy--the WORLD is!

>Other than that, have you cleaned the airbrush with anything nasty that might have got into the paint mix?<

Nope. In fact, the VERY FIRST thing (after a 15-year lapse) I airbrushed was the Humbrol paint and I had no problems. I always clean out my airbrush (a Wren Binks) with lacquer thinner and then run air through it thoroughly to dry it all out and, to insure there is no "color" left, I run the airbrush into a white paper towel until it runs clear as the thinner. AND, this particular problem of "cheese" paint came after successful use of some Testors/Pactra paints (plus similar cleaning-out).

Thanks for the response anyway.

[Weaver]

I'm working my way through a stock of decades old Humbrol tins too, and the failure rate is about 30%. Mind you, some of that's "gone solid" and some of it's "tin rusted through" (they were in a damp basement for ages), but some of it just will NOT recombine, having separated into pigment and carrier, and some of it seems to recombine but then looks cack when you try to use it.

[sequoiaranger]

>I'm working my way through a stock of decades old Humbrol tins too, and the failure rate is about 30%. Mind you, some of that's "gone solid" and some of it's "tin rusted through" (they were in a damp basement for ages), but some of it just will NOT recombine, having separated into pigment and carrier, and some of it seems to recombine but then looks cack when you try to use it.<

All my tins are in good shape. Perhaps my problem was one of the 30%. Mind you, the paint/thinner combination (pic below) worked FINE the first time I tried it (when it was freshly combined). After a few days, as I had said, I tried it again and it spit "cheese" and had glops of pigment. I then STRAINED the glops out with a micro-mesh strainer, and the paint STILL globbed and clogged.

Yeah, looking "cack" all right! 'Tis a shame, because I truly believe Humbrol products are generally superb!

[Hobbes]

Hang on, "freshly combined"? Did you put the thinner into the paint tin? That's a bad idea, because the paint will quickly go bad. The thinner will evaporate in days (even with the lid closed), taking the paint solvents with it and leaving only the pigment.
Always pour the paint into a separate mixing container before you add thinner.
If you use the airbrush cup for mixing: put some thinner in first, then pour the paint on top. Otherwise you get a blob of unthinned paint in the channel from the cup to the airbrush.

[sequoiaranger]

>Hang on, "freshly combined"? Did you put the thinner into the paint tin? That's a bad idea, because the paint will quickly go bad. The thinner will evaporate in days (even with the lid closed), taking the paint solvents with it and leaving only the pigment.<

I don't mean to sound disrespectful, but sorry, but that's patently absurd, in my 50+ years of modeling experience. Are you saying that once opened, Humbrol tins can never properly seal again? I have Humbrol tins from the '60's that I have opened and shut long ago and they have their solvents intact. I turn the tins upside-down so that the paint itself seals the top. No leakage. Your experience may have been from deformed tin lids from prying the top off from one point instead of multiple points (?). Dunno. If I want to use paint with a brush, I leave the paint in the original tin/bottle, but to use in an airbrush, I always transfer everything to another bottle and put a stainless-steel ball bearing in as a shaker/mixer.

>Always pour the paint into a separate mixing container before you add thinner.<

I do that with all paints, actually. I have some "SNJ" mixing bottles that are fabulous.

>If you use the airbrush cup for mixing: put some thinner in first, then pour the paint on top. Otherwise you get a blob of unthinned paint in the channel from the cup to the airbrush.<

Thanks, but I have the type of airbrush that uses a paint-bottle top with a tube that sucks up paint from the bottle itself. I just take the bottle top off and screw on the airbrush uptake bottle top.  Although unable to make and use a small batch, the paint I do use is uniformly mixed already and ready to use.

Thanks for the response.

[Hobbes]

I agree, with the original solvent and pigment you don't have this problem. What I meant was, if you add e.g. white spirit to a tinlet of Humbrol paint, the paint quickly goes bad. I've done this once or twice, and ended up with an unusable tinlet full of dry pigment. I don't know how it happens exactly, but to me the evidence suggested that the paint solvent had reacted with the white spirit, and then evaporated.
I'm not sure this happens if you use Humbrol paint thinner instead of white spirit.
You'll notice that the solvent that's in the tinlet isn't white spirit, it's much thicker.

[nev]

The science is valid - at work when we're having problems drying a batch we blow "wet" nitrogen over it, ie contains Ethyl Acetate vapour.