2024-01-24 - model paint vs. sea water

some time ago i started playing with painting some of the 3D models i print. there are two basic options: enamel paint or acrylic paint. one of these, as they do not mix. while enamels usually have better surface coverage, in practice i use pretty much solely acrylic paints, as they do not smell, so i can use them indoors. however acrylic paint's solvent is water (eg. can dilute it for applying various weathering effects). since i love submarines, the question arose – how would these compare, when exposed to water, for a longer periods of time? to make it harder – let's make it sea water (5% salt). on top of that painting can be done of raw surface, or be primed beforehand. it can also be then clear-coated, or not… so yes – experiment time! :)

i've created a sample test model in OpenSCAD. the model is both simple and have a lot of surface area and edges.

i decided to test 12 samples, and use the following configurations.

print was done in “natural PLA” from DevilDesign. enamel paint was from Revell. acrylic paint was from Pactra (USA). clear-coat is from Motip (for cars). primer is from Surface Primer from Tamiya.

all printed elements were marked with oil marker on the bottom. bottom surface was not painted, though when painting some parts of it got splashes.

zoom in on top 6 elements.

zoom in on bottom 6 elements.

the next day, when all was ready and dry, i've put it into 5% sea water solution, in a jar.

jar has been moved outside (average about 5 deg. C on average, with occasional direct sun) and stayed there for a week. then it was moved inside, as it was about to be subzero outside. then another 2.5 weeks it stayed home (around 23-24 deg. C). every couple of days the jar was shaken and twisted or all samples got removed, photographed and put back. this is the whole even log.

• 2023-12-28 @ xx:xx – printing, numbering, painting…
• 2023-12-29 @ 15:00 – putting in jar and moving outside
• 2023-12-31 @ 15:00 – samples check: no visual artifacts present
• 2024-01-03 @ 16:00 – samples check: no visual artifacts present
• 2024-01-06 @ 12:00 – moving jar home, due to forecasted subzero temperatures
• 2024-01-07 @ 11:00 – samples check: no visual artifacts present
• 2024-01-24 @ 08:30 – samples check: no visual artifacts present

here are photos after removing elements from water and rinsing with tap water.

zoom in on top 6 elements.

zoom in on bottom 6 elements.

after nearly a month in sea water there were no visible artifacts on the samples. surprisingly enough, oil marker had much harder time than any of the paints used (in 1 case i needed to re-draw the number, as it was hard to read otherwise). to sum things up – water and samples badly stink enamel… and that's pretty much it. :) apparently both paint types are ok to paint models that will be put / used in (sea) water.