I've been using a hardware store brand thinner painting and haven't had any troubles shooting with an airbrush. I've recently sprayed a very thin mix of testors flat sky blue enamel and the outcome was a glossy and somewhat uneven sheen. My question(s) is is this something that will always happen when over diluting a paint or are there thinners that will maintain a flat finish? My other question is because of the uneven sheen I was going to attempt covering it up with an acrylic matte, I'm wondering if there will still be an uneven sheen or if I'll be successful in hiding my mistake. The blue is in the interior of a car I'm building so it'll be somewhat hidden already, but I'd like to do it right, or at least cover it up correctly and not make the same mistakes in the future.
Another question I have is masking on flat paint. The body of the car is also flat, which went well. I'm doing my best not to touch it and keep the finish clean. I want to add a few accents to the body and paint the large trim on the side. If I add masking to the flat paint will there be any oils/adhesives/etc. absorbed into the paint? I would like to keep the flat finish without sealing it if possible. I have a few different masking tapes. The green frog stuff, some tamiya tape and something I picked up from tcpGlo for pinstriping 1:1 cars.
Any tips and advice will help.

Sometimes a hardware store thinner (typically brands labeled specifically as "paint thinner" which comes in a quart or gallon can) will cause a chemical reaction with Testors enamel paints that leaves a high semi-gloss sheen even when mixed with "flat" paints. This is especially true when more thinner is added to the mix. For a totally flat sheen, I recommend thinning with hardware store lacquer thinner but this should only be done using an airbrush. Mineral spirits can and often do cause a sheen too. You shouldn't have a problem clear coating with Testors Dullcoat. Many acrylic flat finishes may also work, but I recommend you test first, as sometimes acrylic finishes puddle or "roll up" on top of enamel finishes, especially over semi-gloss or gloss enamel finishes, and if the hardware "paint thinner" in your Testors enamel mix hasn't fully cured, it's highly likely that may happen. I use Home Depot or Lowes lacquer thinners to clean all my brushes, including my airbrushes, but to thin my paints I try to stay with either the proprietary thinners or just lacquer thinner. I have a large can of Testors enamel thinner on my bench that I use just for thinning Testors Paints, several bottles of Tamiya thinner for Tamiya paints, (although I sometimes use Mr. Hobby thinners too), etc. The universal thinner for all is lacquer thinner. I occasionally use hardware store mineral spirits for washes too. I use Testors acrylic thinner or AK thinners for my acrylic paints. I even use lacquer thinner to mix oil paints with, it speeds up the drying time to a point where they are dry in minutes compared to days.
As to your question regarding masking, the low tack painters blue tape should work without leaving residue, but a lot depends on temperature and how long you leave it in place. I prefer using Tamiya yellow tape, and a cheaper method is to use the "kabuki" tape found in the paper/scrap booking sections of places like Michaels and Hobby Lobby-- it's the same thing as Tamiya tape, just cheaper, usually it has some floral paterns or such-- I prefer the striped type as its translucent to some degree. Short of that, you could also use micro scale masking solution, or "Parafilm M" which can be ordered through Micro Mark, or kitchen cling wrap. None of these solutions should affect the finish. I use blue tack and silly putty for masking too, but they occasionally can leave a faint stain or line on dead flat finishes.
VR Russ

Thanks for the info. 'Preciate it.

I'll get some dullcoat for the interior. From what I can see the green zinc on the body looks to be covering the few spots of sanding through the grey primer to the red body well enough for my blood. Will I need to prime or dullcoat the accents or the whole body before shooting flat blue over the green or will flat colors generally not have as much effect from undercoats? A white or silver, or both may be misted over the blue so it may be off of the interior color regardless. I'd like to keep it subtlely different, not far off.

I've been using the gallon of paint thinner from wally world. I did notice that the flat blue mixed funny, like they were repelling each in the cup compared to the mix of yellow, light tan and olive drab I used for the pak40 I'm working on. Way off on the color. It's too green and yellow. I'm hoping to fix that with a filter but it's darkish already. Could a highlight of Payne's grey or Tamiya primer in my case help the sitch? The Model Masters leather base coat mixed and sprayed alright through the airbrush with the same thinner. I had a bottle of older Pactra lacquer thinner for R/C cars and that was the best I've ever used for thinning. It was meant for lexan so it had a flexibility to it and a great bond with plastic and awesome mixes and sprayed brilliantly. I don't think they make it anymore and it's used up. I have Sunnyside lacquer thinner to try. That mixed with tamiyas lacquer grey primer was very "hot" and resulted in some "dusty" shooting and a lot of tip dry so I've been shying away from it. I'll try sticking with lacquer thinner again. My airbrushing mixing ratios and techniques aren't great and I tend to cover larger areas very thin and slowly or I flood or puddle paint trying to do a wet coat. So there's that as well. Maybe I should be misting and working different areas to get coats done in one sitting like the video I watched at one time but I'm not blending well when I try that. Maybe from the hotter quick drying ratios? If I'm going to use lacquer thinner more should I consider an automotive paint retarder?
How do you create a "tight" pinwash? I've tried odorless mineral spirits with artist oil once without a glosscoat and the results were somewhat obvious and spread out a little for rusty bits. I really didn't like the gooeyish consistency no matter how thin I made it. Is there a single hair or micro liner brush technique I could be doing with better pigments or should I try lacquer with oils or something else? I would like to stick with making as much as possible myself. Thinned tars for grease and stains? What's around that has a black iridescent look?

Lots of questions here-- I'll try and answer them, but it may take some experimenting on your part:

[quote]
...Will I need to prime or dullcoat the accents or the whole body before shooting flat blue over the green or will flat colors generally not have as much effect from undercoats?
[quote]

1) I don't think you need to prime any of the accents again as flat colors are fairly forgiving, and will dry fairly opaque.

[quote]
...I've been using the gallon of paint thinner from wally world. I did notice that the flat blue mixed funny, like they were repelling each in the cup compared to the mix of yellow, light tan and olive drab I used for the pak40 I'm working on. Way off on the color. It's too green and yellow... Could a highlight of Payne's grey or Tamiya primer in my case help the sitch?
[quote]

2) I think I'd use a darker shade of tan misted on to change the shade, but I'd stick with the Testor's if that's what you used as a base coat.

[quote]
...The Model Masters leather base coat mixed and sprayed alright through the airbrush with the same thinner. I had a bottle of older Pactra lacquer thinner for R/C cars and that was the best I've ever used for thinning. It was meant for lexan so it had a flexibility to it and a great bond with plastic and awesome mixes and sprayed brilliantly. I don't think they make it anymore and it's used up. I have Sunnyside lacquer thinner to try. That mixed with tamiyas lacquer grey primer was very "hot" and resulted in some "dusty" shooting and a lot of tip dry so I've been shying away from it.
[quote]

3) I used to work in a LHS, and we sold the Pactra for Lexan-- you're right, its OOP, but the important thing is Pactra for R/C cars was much hotter than normal thinner, and it will dry much faster, especially with flat paints, again, I'd stick with proprietary thinners for thinning paints, and not mix them, as that can cause different problems in application.

[quote]
...Maybe I should be misting and working different areas to get coats done in one sitting like the video I watched at one time but I'm not blending well when I try that. Maybe from the hotter quick drying ratios?
[quote]

4) I'm not quite sure what you mean by "blending well"-- do you have too much overspray? Is your paint running into the base coat? Usually overspray is mixxing and air pressure problem, running into the basecoat is a symptom of too much paint.

[quote]
...If I'm going to use lacquer thinner more should I consider an automotive paint retarder?
[quote]

5) You shouldn't need a retarder while using lacquer thinners for model applications, and I'd be very careful about using automotive retarders like PPG, as they have nasty issues if not sprayed properly-- one of which is forming strings or spitting (Ive used PPG brand before) they need to be used only with their own proprietary paints and thinners-- automotive lacquers today are primarily acrylic lacquers-- and are no relation to water based (Mig, Vallejo, Lifecolor) or lacquer based (Tamiya, Gunze) model paints.




6) A "pinwash" is really a term for a light application of thinner based material (more thinner than paint) in fine cracks and crevices. The best results are done with a fine brush, using a dissimilar paint to the basecoat (oils or acrylics over lacquers and enamels, or vice-versa). They dont need to be done over a glosscoat, but it helps with the cleanup-- when I do a pinwash, I keep a small bit of cosmetic sponge handy with just a touch of thinner moistening the sponge (thinner depends on the pinwash), which I use to clean up any "mistakes". You can also turn you airbrush down to its finest setting and go over the dry "pinwash" with the base color to blend it in.

---Finally, you mention AB tip dryness and "blending" issues-- these sometimes are more of an air pressure issue than a paint issue, if you have a pressure regulator on your compressor, experiment with different settings and mixtures of paint. I typically airbrush most paints at 60% thinner, 40% paint at a pressure of 10-14 PSI. I adjust the airflow from there for thinner paints. I seldom airbrush anything over 18 PSI, except for Floquil Silver and Tamiya Gloss White-- Those two colors I find can be shot at much higher pressures-- It's something about the fine pigment in them.

VR, Russ

And all along I thought I was keeping the Q's to a minimum ;P It's been great of you to take the time to answer my run-on questions. I realize now it probably makes it a pita to reply to. Lately life is like a run-on point and shoot at a penny arcade with that damn duck hunt dog laughing all the while. Today's larf was a propane torch tank's safety valve? leaking and flaring up while I was using it to light the brush pile in the pit. Been awhile since I ran that fast and only to find someone took the hose reel and put some pocket hose contraption in it's place. I had to find 3 other hoses to get there while the thing was burning away. I thought it was gonna get ugly. So I finally get around the sheds to pop around the corner hiding with the hose and the flames go out. Good times... lol

I'll be more setup and prepared for modeling experiments soon, and then, and only then, less questions. Muahaha!! Jk jk I did finally get an exhaust setup for my booth so I can paint with the rugrat in the house now which helps immensely. Stupid me didn't even think of a downdraft table until after I finished everything else.

Anyway. My blending issue seems to be that the paint will dry too quickly and there is a thicker than wanted layer of paint in the end. It can be an uneven slightly textured finish. Bad atomization from wrong ratios and pressure? I've been shooting at around 10 psi but probably under. I used to shoot at a higher psi but it seemed to use up the paint cup so quickly. I'll make a baseline 60/40 for ratios and work off that. I'm using a paasche vl with 3 different needle/tip sizes. Most common for me is the 0.3. so far. I did debur and chamfer parts that weren't machined or finished correctly to hopefully improve airflow or reduce turbulence. Seems like a sound brush so far. The question here is...

It sounds like you're describing "orange peel" if the finish is "slightly textured"-- this is an effect caused by paint drying at the end of the airbrush or in the air-stream before it hits the finish. It's cause is usually too high an air pressure, holding the airbrush to far from the work, or improper paint mixtures-- or all three. Another cause can be the "hotter" non-standard thinners it sounds like you are using-- they can dry as they come out of the nozzle. That's why I recommend the proprietory paint thinners for mixing.
VR, Russ