Why is it that plastic that’s painted with flat colors seems to be much more brittle and breaks so much easier than gloss painted plastic ?. Is there something in the paint that weakens the plastic ?..
Tracklayer
It’s probably the type of plastic… You’ll probably also notice that the ‘shiny’ pastics don’t glue and paint very well… Otherwise known as Engineering plastics, very common of which in our hobby is Delrin… The ‘non-shiny’ plastics are usually some type of styrene.
Hey rolleiman.
I first noticed this problem when I was building model cars, ships, airplanes and so forth which are made of styrene. Most flat painted details tended to break easier than those that were painted gloss.
As for model railroading. I’ve noticed that Bachmann and Walthers rolling stock stirrup steps and grab irons that are painted flat are really brittle and break off extremely easy.
I was just wondering why, or is it just my imagination ?..
Tracklayer
It’s part of Murphy’s Law:
“The smaller the part, the greater the likelihood that the last time you touch it before setting it in place on the layout, it will break…”
“The glossier or perfect the paint job, the greater the odds that your finger will find the most obvious place to rest…”
“The more careful you are removing a delicate piece from the tree, the greater the likelihood that it will snap… right in the middle…”
It’s your imagination. I’ve been painting plastic models since the 1960’s and have never encountered such a condition. However, it may be the type of paint you are using (water based vs. petroleum based). But whether it is flat or glossy has no impact on the durability of styrene plastic. Water based acrylics will have the least impact on plastic (my biggest objection to them is that they tend to chip or rub off), petroleum based enamels such as the testors brand stick to the plastic better but usually don’t attack the plastic. Most laquers do bond with the plastic, some attack it, and can alter the plastics properties. Bare plastic exposed to sunlight will become brittle with time. There are also apparently some variations in styrene plastic from different manufacturers. Some of my older models from the 1970’s have become brittle with age while others have kept their original properties. Tamiya from Japan uses a plastic that is relatively soft and pliable while Hasegawa from Japan uses one that that is firmer but breaks more easily but both are styrene. So I think its properties of the plastic itself and not flat or glossy paint that you are noticing.
Bob DeWoody