We’ve previously covered how too much primer and paints block all light from shining through EVA foam and concluded that if you were going to do that, you’d be best served avoiding primer and minimizing paint. This follow-up post dives into that concept and explores the results you could get by doing so.
Let’s jump right into it.
As previously, the first thing I did was prepare a test piece using 2mm EVA foam with a density of 45 kg/m³ (results should be similar with 1mm of 100 kg/m³). Unlike the previous test however, no primer was used this time, and no three layers of white paint.
I started by applying pieces of masking tape (cut into random shapes, for effect) to the areas I wanted to keep clean. Then I applied a cheap yellow paint across the entire surface of the foam, which without heat-sealing and without primer, quickly sank into the foam and kept the surface dry for the next layers. I used an airbrush to apply layers of orange, orange-red, and finally red, trying to work outward from the center of the masking tape. I filled up the remainder with brushed-on brown and black acrylic near the edges, before finally removing the masking tape:
This worked out surprisingly well, given the foam wasn’t treated in any special way, and the paint was applied directly on top of it.
Since we previously determined that light will shine through thin EVA foam just fine if there aren’t too many layers of primers and paints in the way, and we skipped the primer, used less paint, and kept the “shine-through” areas completely clear of everything, surely backlighting this will have a much better result?
Weeeeell… yes and no:
As you can see, light does actually make it through now, and even without a lot of effort, the effect is pretty sweet. That’s good. What isn’t as spectacular is that so because of the reduction in layers, light now also comes through in all the places you don’t want light coming through. And that’s just not acceptable.
There’s a few ways you can work around this.
One obvious method is to use primers and base paints everywhere else, but getting spray-on primer applied in a way that skips the masked areas is a challenge in and of itself. Remove the masking too soon, and the primer will spread (either by viscosity or by you touching it by accident). Wait just seconds too long, and you’ll have a solid skin over both the foam and the masking, making it impossible to remove without touching the primer layer. After all, helping to bridge such gaps and deliver a continuous surface is part of what primer is meant to do.
I’d suggest the next best thing: adding layers behind the thin foam. It’s unlikely you’d use thin foam exclusively and without a thicker supporting structure anyway. So that’s what I did.
Of course with a thicker foam backing it, no light will come through. So you’ll need to make some holes that let light through that match the shapes on your thin foam.
If you’re doing this for any serious project, I’d very strongly suggest that you create the masks digitally. You can then either print the masks out on regular paper and trace it onto masking tape by hand, or have it cut out by an automated cutting machine. This will give you the best possible reproduction of the shapes you wanted, with the greatest consistency.
There’s no reason you can’t do it by hand, though. For example, for this test piece, I simply took a piece of paper, put it on top of my painted EVA foam, and lightly traced the edges of all the lines. This doesn’t give you the accuracy the above methods would provide, but it’s good enough for this test.
Once I finished tracing the shapes, I just taped it to a piece of 1cm thick EVA foam floormat I had lying around. I was then able to just take a knife and cut out the shapes from the foam.
The result wasn’t pretty, but it didn’t really have to be. It only has three purposes: to provide structure, to let light through the cut holes, and to block light where there aren’t any holes. Once I was done cutting out the shapes completely, I adhered the thin foam to this structural backer piece with contact cement.
I didn’t managed to perfectly align the two pieces, but again, this was just a test and I didn’t try very hard. To help prevent hard shadows when the light sources don’t align exactly, I went back in with a knife once the two pieces were solidly connected and manually beveled the edges. You may or may not be able to do this on your projects depending on the shapes and sizes of your foam, but it does help a little bit:
Here’s what the result looked like. Not bad for a throwaway test piece, actually:
But you may notice that this piece isn’t lit.
I was getting pretty tired of just using a bright white LED for testing, so I decided to try a little something fancier. Using an Arduino Uno, I manually designed a custom “living fire inside” effect. My phone’s camera doesn’t capture the difference between yellow and orange very well, especially during gradual changes, so please excuse the poor quality… but the end result is pretty “hot”:
And no, I’m not apologizing for that pun.
I hope you’ve enjoyed this follow-up look at what can be done with EVA foam and LEDs, and an example taste of the effects that could be achieved by foregoing some of the ‘traditional’ steps and changing your approach to a project.
Thanks for your support, and remember to have fun!
If you like posts like this and want to keep them coming, please consider [supporting me]! Even one-time donations of $1 help out. You can also use Patreon for monthly donations, or donate any books you may have that I could use as reference materials. I love videogame art books!