I noticed when making a compact laser for the purpose of blasting things with heat (because blowing stuff up is fun!)
...Photons seems to be able to travel through solid substances, including Cline, I think. But when making stamps, I believe Powder Toy becomes confused. The dots of C-line that have photons on top of them get lost in translation, as well as in upload.
I'm not sure if it's possible/easy to fix this, but for now I can't complain. It makes stealing my things on my uploads a bit more difficult. In order to finish my laser I had to make a stamp of C-line after it had already touched Photon so that it wouldn't eat the surrounding Void, and then add the Void back in (while paused), after pausing a couple of times to wait for a lucky moment when there were no photons on top of any C-line.
So it doesn't technically break anything, I suppose. @_@
At the moment, photons can travel through Glass and Clone, the reason for this is that they can sometimes get stuck in clone. They may also be able to travel through thin walls of any solid, use thicker walls if this is a problem.
I've found it's easy to make a sort of focus (despite not being able to bend photons.)
By making a grid of Clone and then stamping while paused, you can narrow the direction of photons using Void. Abusing how Photons can pass through Clone, you can make lines of clone one pixel thick lined with opposite lines of Void. This way, every other pixel produces the same direction of light. ^^
This is an absurdly long barrel, but it produces a stream of photons in only one direction without any gaps at all. You can add Uranium and WhiteHole chambers to produce heat to make the photons hot enough to melt glass, even.