paint storage - flow aid & thinner

[tom q vaxy]

Q: any long term effects of adding flow aid & thinner to a bottle of paint vs using it at the time of painting?



several sources of decanting odd shaped bottles into a consistent 17ml dropper bottle suggest using the above additives in order to facilitate transferring and it runs contradictory to what i have always been lead to believe.

https://youtu.be/p_OR2ZeMKNU?si=nGD50H7SgLnuEm-h

[Bob Cleek]

I'm not aware of any negative effects of adding thinners or conditioners to paint which is thereafter stored long term. That said, "long term" is a relative concept. Anything less than an air-tight seal and the absence of any oxygen in the paint container (e.g., a partially-filled can) will permit polymerization to occur, causing skimming and eventually the hardening of the paint. (An oil paint can may be purged of oxygen by slowly filling it with propane from an unlit plumber's torch until the heavier propane displaces the oxygen, after which the can is securely sealed.) The more air, the faster this will occur. Additionally, long term storage will permit the pigment to settle in the bottom of the container and it may eventually become so compacted that it will be near impossible to stir and redistribute evenly in the liquid medium without mulling it again. 

 

It's my guess that as much as ninety percent of the small bottles of model paint, fingernail polish, and touch-up appliance and auto paint, and the like end up hard as a rock by the second time a consumer attempts to open the bottle and ends up tossed into the trash. Buying pre-mixed paint in tiny amounts is the most expensive way paint can be purchased and buying "ready to use pre-thinned "airbrush paint" is the most expensive way to buy paint thinner! This is one reason why some modelers have switched over to mixing their own paint using tubed artists oils and acrylics which have long shelf-lives and tend not to harden in the tube because there's no room for exposure to air nor any dryers added to the tubed paste. (The end user thins and conditions tubed paints themselves.)