L40 Mixed Color Cube Various size For Home Or Office Toy Science Learning Cube Easter Prism Desktop Toy Home Ornament (WHL #76)
Electronics-free interlude for today.
That shameless advertising video from Vsauce
kickstarted my interest in those color-mixing (well, subtracting) “CMY” cubes.
A quick check of their website reveals their equally shameless pricing of 20/30/70 USD for 30/50/95mm cubes, ten bucks on top for international shipping, and, outside of their control, the local government slaps on another shameless 19% of VAT. Well, that’s 36, 48 or 95 USD=EUR for a novelty gadget. 1.32/0.38/0.11 € per cubic centimeter, to be precise. OK, cool but a bit steep.
While they don’t say much about materials at all, it’s probably some optical grade acrylic that is “diamond polished to perfection” (wank, wank) and then coated directly. The same material as is used for educational prisms and the like, those are typically not made from glass as they wouldn’t survive for very long.
I don’t think it’s an adhesive film as that would be easy to peel off, and they don’t have any corners and edges to wrap it around to avoid that. The Vsauce video actually includes a quick explanation of what the individual faces do, so it is not dichroic mirrors that are also sold, but have a different effect and a visible internal structure as demonstrated here:
So…what does China have to offer? 
Fake CMY cubes of course. Which leads me to the very first item that I have successfully returned to an AliExpress seller as far as I can tell. 14.01€ including shipping and free return (I made sure that was offered on this very product) in early May. This translates to 0.16€/cm³, so it’s actually more expensive than the largest original cube, but only 42% (hehe) of the similarly-sized classic CMY.
This was used as their promotional material:
The picture is for reference only, the actual product is mainly received. Due to the shooting angle and shooting method, the color of the product may be more beautiful.
Turns out: It wasn’t more beautiful – it didn’t even match the weirdly photoshopped advertisement photo. And that itself was one of the better ones, since many other sellers use real photos showing their subpar quality products (which are to be avoided right away) or just enhance those photos slightly to be in a grey area. When I shop for questionable items, I make sure to buy from the seller that makes the boldest claims. That’s to be in a better position when it comes to a guided dispute in which I can show the stark contrast of advertisement photos and real life product.
So, this arrived:
It’s not quite the same as promised, right? (Yes, it shows up a tad better in sunlight due to better spectrum, but not by much)
I don’t care much for the chamfered edges or the slight imperfections of the material, but the color changing effect is the selling point of that thing – and it clearly does not mix well.
✔ THE MOST SATISFYING GADGETS – Color cube is a translucent acrylic cube with cyan, magenta, and yellow on each surface. As the angle is changed, the light through the cube mixes into green, red, blue, etc. When all three colors are mixed from the corner, you can see the most colors and a smaller cube is created inside the cube, which definitely blows everyone’s minds!
Judging from e.g. the bright red specks from this very angle (see photo below) where light skips one absorption layer as it enters through a clear edge, I think the overall problem of those Chinese copies is the spectral performance of their coatings. Many cubes can be seen with large black volumes, so total absorption of light, where the original one just does that with all three filters present (internal reflection is a bitch). Of course the graph from the first video doesn’t have to be close to the dye used, but even then two passes at 80% transmittance make one third of the wanted light band go to waste, in addition to filtering everything else. If the Chinese copies only achieve let’s say 60%, that’s two thirds of the desired light gone and the entire thing looks dark and dull.
They also probably have a much worse overlap structure of their three colors, so a more narrow band of the spectrum will pass, but with a much shallower frequency response. It simply won’t have a sharp cutoff as the material shown above, but wash out significantly more. Optical attenuation is pretty similar to electronic attenuation via filter circuits, so in analogous manner to a higher order electronic filter that requires more circuitry than a simple RC filter, a crisp optical filter requires more chemical engineering and better processes than the cheap “will do” stuff used here. Well, it unfortunately shows.
Characterizing these would be great, but my simple spectrometer doesn’t have the resolution to do so, nor do I own a reference light source for a fair comparison. Maybe one day 
Safe to say I actually tried the free return option and it did work – I got a Hermes label from the AliExpress website, printed it and boxed the entire thing a little better than it originally was, and returned it to a random warehouse in Germany. A couple days later, the entire sum was refunded.
Well, I’m usually not the kind of guy that returns items for a full refund, but that thing really looks like a cheap copy. As much as CMY likes high-gloss product photos on their website, 3rd party videos confirm that the product actually does have this crisp cyan-magenta-yellow filter effect that neatly blocks out bands to achieve striking colors. This China copy simply doesn’t, and AliExpress, eBay and Amazon are full of it.
I’ll keep an eye on those products, maybe they’ll improve over time and/or the original product comes down in price when it’s no longer a hyped novelty on YouTube… 
