So I polish two sides… on one I put 1 of 4 strands of leds on for testing (on that side). 

I was able to get some FTIR results but they where very faint.

But I’m not sure if I polished enought.  I had an electric sander and 4 different grits of sandpaper up to 600… Then some metal polish.  It looks pretty good (and when I cut it an angle, it I can see through it well… tested before for possible angled leds… scrapped that idea)…

The only part I’m worried is there are some tick marks… but not many.  Very small.

I can see light at the other side of the plexi… so I’m guessing its all good.  But its not super duper brite like I’ve seen others.

Number of leds the problem?  I’m solving that.

That I’m not preping the LEDS by cutting / polishing them flat?

The LEDs aren’t even always touching the plexi (rounded end didn’t seem all that important).  Will that make a difference?

Should I do a better job polishing?

Any clue or just play with it?

Thanks for any input

well there is even 2000 grit sanding paper, so you could get some better results on that part i guess, afterwards you can polish it with copper or silver polish, those are basically like really fine sanding papers. you could also try flame polishing them with a very hot flame to make them more transparent, but that is something you just have to test. I personally had satisfying results with just sanding and polishing. Because if you flame polish it to long it might get black or air bubbles

I’d say theres really no need to go with 2000 grit when your brasso metal polish will finish it.
I used about 200grit for only a few minutes to smooth it to a roughish white edge (use a sanding block, its important to get it dead flat).
Then switched to 600grit, did this for a while longer to get it to a smooth white edge.
Then used brasso metal polish with a kitchen cloth for a good while, maybe 5-10mins to polish one edge. You don’t have to go circular, linearly up and down the length is sufficient but it cant hurt to go circular. You should be able to see only a few REALLY small scratches looking REALLY close at it (I’m short sighted so I just took my glasses off to look closely at it!).
You can really compare the top layer of the acrylic with your polished side and see a good likeness in finish.

Aside from that provided it isn’t white edged or really scratched, I’m sure it doesn’t matter, it’ll still let the IR light in to good effect.

As I’m exploring, its not down to the polish, but rather what you do with the layering of different materials on the acrylic that gives you good FTIR effect.

Stu

Ok, I polished it for only a minute at most.  I’ll try going over one side again for a bit and see if I can tell a difference.

Also, I have some of the silicon sheet + some rosco.  I haven’t put it on yet.  I’ll see if that makes a big difference.