I think I ran across a thread about this many moons ago but was unable to locate via search, so forgive redundant posts/questions.
Yesterday a friend came over to help me airbrush the tracks in my yard. We mixed a batch of PolyScale RR Tie Brown with PolyScale thinner at about 40/60. This was mixed with a stirring stick - not shaken as Bond would say [:)]
Pressure was set at about 20 psi and we immediately had problems - no paint, just air from the Paasche H. We then shot some distilled water through the airbrush just fine. After several more attempts and with re-cleaning the airbursh, we examined the paint in the mixed bottle, the paint was congealing in the bottom.
We then mixed another batch and immediately notice that within minutes of adding the PolyScale thinner to the RR Tie Brown, the paint was congealing. I had had this RR Tie brown open before and it has been in my garage since about Jan. I had temps of 90 in the garage for many days this summer.
PS. I had some craft acrylic paints that I had also previously mixed up to a RR tie brown color. This was thinned about 50/50 or so with plain old window washer fluid. We completed most of the track but ran out of the “special mix”.
Is the PS paint no good or has the PolyScale thinner gone off ? Or, should I never consider a career in painting.
All paint after it has been opened has a limited shelf life. Some say it’s due to the moisture in the air that gets trapped in the bottle upon resealing the cap. Variations in temperature have an effect too.
Some people have tried storing previously opened paint bottles cap side down which is supposed to prevent additional contaminated air from entering.
Also as paint is used there is more air in the bottle to speed the loss of quality. Polly Scale paint is about as good as any but once it has started to turn no thinner will reverse the process.
O.K, I’ll answer here before I leave the forum until the Christmas Holidays.
Be aware that sometimes the Polly Scale reducer is the source of the problem!
Happened to me last year as I was weathering some freight cars. The paint kept turning to “jelly” and I thought it was defective. I then cleaned out the airbrush and decided to thin the Polly Scale paint with a mixture of distilled water and 70% alcohol. Wala! No problem! Paint was fine. A friend of mine told me that he had heard of occasional problems with the Polly Scale thinner.
As for Polly Scale paint…some of my jars are 3 years old. Paint is still good. Always clean the jar top openings before capping. Makes a big difference in keeping air from seeping inside.
I still have the bottle of Poly Scale thinner, almost full, sitting on my shelf. I now use distilled water and/or alcohol with no problems.
I concur with antonio and I’ve got some bottle that are probably around 5 or 6 years old and are still good.
We’ve got soft water here so I just use tap water and alcohol. The amount of alcohol isn’t really critical, I use somewhere between 10 and 20%. It’s mainly there to cut the surface tension, (as a wetting agent), so the paint doesn’t bead up - just like wet-water for ballasting.
If you have hard water (high mineral content) you’d best use distilled water.
Two things I don’t see mentioned often enough here on the forum concerng painting with acrylics:
One should never paint from the bottle the paint is stored in. Any paint that dries in the cap can fall back into the jar and then be sucked up into the airbrush and clog it up.
Secondly, when you pour the paint off into a clean container, (I use McDonalds little condiment cups - I grab a few whenever I go), screen the paint to remove any of those dried particles or any other solids. For screen material I use tossed stockings.