Diffractive Chocolate | Hacker News Reader

Diffractive Chocolate

wp.optics.arizona.edu

250 pointsjoebig67 comments

One of the things I appreciate about HN is that discussions often acknowledges the pioneers. Way back in the early 1990s Eric Begleiter started Dimensional Foods to commercialize edible holographic technology. He gave a memorable demo at Thinking Machines Corp. where, in addition to rainbows from diffraction sheet molded foods, he showed some simple rendered 3D scenes floating in chocolate illuminated by a slide projector. Very impressive at the time when he broke off a chunk and ate it. The short-term idea was to give a rainbow sheen to breakfast cereals, but I think longer term there was talk of using holograms to distinguish and layer information on medicines. Made quite an impression at the time.

https://web.archive.org/web/20150527050715/https://www.nytim...

If you don't mind me asking - what were you up to at Thinking Machines at the time?

I tried this in the early 90s off the back of a short article in Scientific American about chocolate holograms which was almost certainly about the same company. It worked, and I think it would have worked a lot better if I knew more about tempering chocolate.

It struck me at the time that using holographic foil as a mould would be the natural next step.

I've got a vague memory of a chocolate record being made as an art project? The needle abraded the surface so it wasn't really playable more than once.

Samy Kamkar, a computer security researcher whose work is discussed on this site, generated some coverage with his iridescent chocolate a few years ago. But the article and HN comments point to prior art.

https://news.ycombinator.com/item?id=23128379

https://www.nytimes.com/2020/05/21/science/chocolate-irisdes...

I've done this! You can also cut a small square of diffraction grating and put it on top of a hardening chocolate candy (like an enrobed square of ganache) to make decorate a completed chocolate: http://whoisgood.dog/img/chocolate-diffraction-picture.jpg

Also tip: easiest way to temper a pot of chocolate is with an electric hand-mixer. Wait until it's 32C, mix for fifteen seconds, bam tempered.

It's pretty easy to put the chocolate into a tempering machine, push a button, then walk away, too.

It's pretty easy to just order the chocolate and just doing nothing yourself...

You do understand that a trick is something different than buying a machine for the job right?

... Using a hand blender is using a machine for a job too, isn't it?

GP's point is that responding to an aside about how to do something with a snarky "or you could just buy a dedicated machine" will come across as obnoxious. This should be obvious to you or anyone.

What's obnoxious is someone claiming they have found the easiest way but then refusing to accept an easier way.

A tempering machine costs hundreds of dollars and wouldn't fit in my apartment kitchen. The hand mixer was ten dollars and fits in my drawer.

Also, this is advice to anyone who wants to try it for themselves. Isn't "buy a hand mixer and some diffraction film" an easier onramp than "buy a whole tempering machine?"

It's using machine for the job, which is different than buying a machine for the job.

A hand mixer is cheap and has endless uses. A chocolate tempering machine has a single purpose. Makes sense to get one if you're making chocolate in large quantities.

You can't buy tempered, melted chocolate easily. If you want to cast it into a mold, you must melt and temper it or melt it very carefully.

I found the easiest way was vacuum sealing some chocolate and sticking it in a souvee at 92f overnight. Agitate a bit after it's melted and a while before removing it from the warm water. I use the method for making tempered cocoa butter to use as seed in my tempering machine. The exact temperature varies by type of chocolate. The trick is getting it just below the point that type 5 crystals form. It's perfect to make seed chocolate for when I use the tempering machine, saves a lot of time and there's the convenience of having a big pool of chocolate for molding, it's better to have a bigger pool than you need so that when you pour out molds you can do it directly into the working pool.

https://www.youtube.com/watch?v=UsDnkrDvkBo

Ben from Applied Science has a good video going over the same topic.

You can also find the same thing naturally in roast beef when you cut against the grain resulting in even microstructures.

https://www.mdpi.com/2304-8158/2/4/499

Similarly they now have diffractive 3d printing "beds" that leave a chromatic layer on the bottom of your 3d prints...

https://store.bambulab.com/collections/bambu-build-plates/pr...

If you can cast a diffraction grating into chocolate, it should also be possible to cast a reflective hologram. Holding a block of chocolate up to light and seeing a 3D image would be pretty cool.

https://www.npr.org/sections/thesalt/2014/06/14/321816570/ho...

Thanks! Nice to know that it can be done.

It is obvious that if you correctly add pieces of something like this to a viscous medium (so that the pieces are on the surface of the medium), you will get a viscous material with a visually observable diffraction effect:

https://bartovation.com/product/other-lab-supplies/diffracti...

The other thing is unclear:

Why gnaw on diffraction sheets?

Will this make chocolate taste better? Will this improve your health? It's all very exciting and mysterious.

The reason to use chocolate is that it is able to form a diffraction grating, so you don't have to eat the plastic.

Given the surprisingly small feature size achievable, small enough to get diffraction, I wonder if anyone has tried making a playable CD out of chocolate or sugar.

You'd need to move the laser and keep the disc stationary I wager, otherwise is it even chocolate anymore if it can stand the forces?

A vinyl is doable.

A CD probably not. The refraction doesn't need to be aligned etc.

Putting it on and scanning it perhaps but not a one try it life

I like your way of thinking :-)

A CD as a reflective coating to distinguish the pits, I don't know if that's mandatory though. Very thin gold foil is edible though (it just passes through the intestines, being chemically inert), so maybe a sugar disc coated with gold could be made to be playable, and still be edible?

As for the base material, I'm pretty sure that sugar has the better mechanical properties compared to chocolate. If you get it perfectly round and spin it up slowly, there shouldn't be too large forces acting upon it.

This is cool. I wonder how you ensure that your mould is made from food-safe materials. Presumably gratings are usually just cut glass, so that should be okay? They are not part of the usual food-safe supply chain, though. I guess to would be tricky to obtain the proper assurances if you wanted to do this commercially.

A mass producer would simply test the standard materials and verify. Molding is a well understood industrial process.

https://archive.is/Lphsl

Diffraction gratings are amazing. Is it possible to make one with a 3d printer?

You can order them super cheap and in bulk from a variety of retailers. Ranging from simple toy things to rolls of it

Link me?

https://duckduckgo.com/?q=buy+diffraction+grating+sheets

The feature size is pretty small for diffraction gratings. There are printer beds that will do the same to the bottom of your print as is done with this chocolate. None of the hobbyist models could get even close. The feature size is somewhere between 1 and 10 micrometers which is a couple of orders of magnitude finer detail than most 3d printers.

They are normally manufactured with other methods, but here’s a paper about printing them https://asmedigitalcollection.asme.org/IMECE/proceedings-abs...

So it’s possible, I’m sure they aren’t the only ones to try it.

no, not really -- BUT -- you can print onto the top of a grate to apply that surface finish to the bottom of the print.

It's a neat thing to do when you're printing phone cases or something similar.

Why haven’t chocolatiers exploited this to make really unique pieces?

Too busy exploiting trafficked child slaves? https://www.bbc.com/news/world-us-canada-57522186

In all seriousness though, this would be pretty cool and I'd love to try it. I suspect that some of the problem is just that companies tend to constantly push to deliver the bare minimum while charging the most. Holographic chocolate would take more money to make and companies are always trying to charge you as much as you're willing to spend for chocolate while giving you the lowest quality/effort product you'll still pay for. While I wouldn't expect to see something like this showing up in the candy aisles of your typical grocery store smaller fancier places will be willing to do it and charge a premium

https://www.brunnershop.com/en/Frame-Moulds/Holographic-choc...

It isn't a matter of money, it's just too delicate to sell: unless you distribute bonbons or tablets still in their mold, to be cooled and extracted just before eating, even mild heat applies a lowpass filter to micrometer scale surface features instantly and unrecoverably.

In my experience, it's three things:

1. You need really good surface contact to get the diffraction on, so you can only really apply it to flat, uncurved surfaces

2. You need to apply it while the chocolate is hardening. If you're using a mold, you cast the chocolate upside-down so only the base is exposed during setting. You can't diffract the part people will actually see.

3. The effect is really fragile. Chocolate melts at around body temperature, so if you hold the piece for too long, the diffraction disappears. I've been able to transport diffractive chocolate in a padded box but don't think I could wrap the chocolate directly.

I assume the transportation is the real problem. Even taking this sort of thing home from a store might lose the effect.

I can get a pretty decent temper on chocolate and I make bonbons once in a while, but I have still found that you can lose fine surface details with a temperature that is a comfortable "room temp" for humans.

Makes sense, thank you.

It's something that would need to be created in a retail confectionary for immediate consumption. And, people might demand refunds when the slightest heat ruins it should they attempt to transport them without a cold chain.

#3 can be solved by keeping it frozen.

No, because as soon as you take it out water from the atmosphere will start to condense on the surface and destroy the diffractive properties.

Would loads more sugar help? it would be more candy than chocolate.

maybe a thin sugar shell around regular chocolate

There was a Swiss startup called Morphotonix that made holographic chocolates [1]. The company and its holographic-imprint tech are still around, but they've moved on to other markets. That suggests they just couldn't get prices low enough to make it appealing.

[1] https://www.npr.org/sections/thesalt/2014/06/14/321816570/ho...

I feel weird about edible artwork. Do I buy it for food or do I buy it as a piece of art? How many of it would I ever buy? Then there's also the added costs to both sides. It might be very niche.

If plating is ever a concern to you (which it almost certainly is) then in a way you already eat art.

The parent comment means "plating" as in the art/activity of arranging food on a plate [1]. Not, I presume, the manufacturing process of coating something with a thin layer of metal.

1: https://www.cozymeal.com/magazine/plating-food

what the heck are they talking about in the linked article? each color of light travels at a different speed?

> White light can be separated into all seven major colors of the complete spectrum or rainbow by using a diffraction grating. The grating separates light into colors as the light passes through the many fine slits of the grating. Each color travels at a different speed and therefore has a different angle of refraction when it hits the grating.

Yeah, that's a thing. 3Blue1Brown did a video on it a while back:

https://www.3blue1brown.com/lessons/prism

It's part of a larger series that starts here:

https://www.3blue1brown.com/lessons/barber-pole-1

why did you think it happened?

refraction angles are wavelength dependent, i thought...not the fraction of c by wavelength of photon.

from the wikipedia article on dispersive prisms, for example, though i asked above because i remember this from physics at Fermilab in high school.

> The refractive index of many materials (such as glass) varies with the wavelength or color of the light used, a phenomenon known as dispersion. This causes light of different colors to be refracted differently and to leave the prism at different angles

Frequency is constant, wavelength changes and so does velocity, from wikipedia refractive index

> The refractive index, n, can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is v = c/n, and similarly the wavelength in that medium is λ = λ0/n, where λ0 is the wavelength of that light in vacuum. This implies that vacuum has a refractive index of 1, and assumes that the frequency (f = v/λ) of the wave is not affected by the refractive index.

They travel c in vacuo but not through different media.

Yeah, the author absolutely confused this with transmission grating which works by transmission rather than reflection.

transmission gratings also do not work by dispersion

With a diffraction grating, all colors travel at the same speed, but some light waves reflected off/transmitted through the grating end up taking a longer path to reach the same point in your eye, and depending on the wavelength, that length difference causes constructive or destructive interference, amplifying some colors and suppressing others.

Colors traveling at different speeds through a medium is the usual explanation for color separation through refraction, but it doesn't really help for understanding diffraction.

It's indeed not correct... but it diffracts so some of the light lands on your eye later because it's angled differently hence the colour change... just guessing. I'm not a physics major.

Yes; a dispersive prism (https://en.wikipedia.org/wiki/Dispersive_prism) is a simple example of this (both prisms and diffraction gratings are used to break light up into its spectrum). The fundamental physical mechanism is known as "dispersion": https://en.wikipedia.org/wiki/Dispersion_(optics)

The backstory of diffraction gratings is part of the ongoing story of precision. The first ones were created shortly after Newton's use of the prism to demonstrate dispersion, and by the late 1800s, https://en.wikipedia.org/wiki/Henry_Augustus_Rowland was quite good at making high quality gratings that were used in astronomy to figure out some of the most fundamental details. They were highly sought after- effectively he was the only person who could make high quality gratings for a while (and he shared them widely).

If you really want to go down the rabbithole, see https://en.wikipedia.org/wiki/Dividing_engine (fans of the screw cutting lathe will appreciate that the same technology is used) and https://www.edmundoptics.jp/ViewDocument/MKS%20Diffraction%2... and http://snl.mit.edu/pub/papers/WP/Nanoruler-White-Paper.pdf

however, diffraction gratings do not use dispersion, so the page is confused

this error is not contained in the tech ingredients video the page links; unlike, for example, nighthawkinlight, tech ingredients is careful to get the science correct

Dispersion is the name for the process of separating the light into individual frequency components but there is more than one mechanism. The term 'dispersion' to refer to what diffraction gratings do is already well established.

usually the term 'dispersion' is contrasted to what diffraction gratings do. 'dispersion' normally refers to the frequency-dependency of phase velocity in a wave medium, which can result in separating waves into separate frequencies but does not always (for example, a pulse train traveling through a one-dimensional dispersive medium is a case of great practical interest). but it's true that from time to time people do use the term 'dispersion' to refer to separating light into individual frequency components with a diffraction grating. it just isn't the normal meaning, and it isn't one i'd seen before

The person you're responding to is correct.

Dispersion is the result, refraction and diffraction are ways that it can happen.

> The grating acts as a dispersive element.

https://en.wikipedia.org/wiki/Diffraction_grating

the comment you are replying to already explains that people sometimes use the term 'dispersion' in that way, but puts it in a broader context:

> but it's true that from time to time people do use the term 'dispersion' to refer to separating light into individual frequency components with a diffraction grating. it just isn't the normal meaning, and it isn't one i'd seen before

for the normal meaning, see for example the page dekhn linked above to explain it, https://en.wikipedia.org/wiki/Dispersion_(optics)

> In optics and in wave propagation in general, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency;[1] sometimes the term chromatic dispersion is used for specificity to optics in particular. (...) In optics, one important and familiar consequence of dispersion is the change in the angle of refraction of different colors of light

diffraction gratings do not in any way depend on this phenomenon; they just replicate the consequence through a different mechanism. so where dekhn said, 'The fundamental physical mechanism is known as "dispersion"', linking to the same page i linked above explaining the mechanism that diffraction gratings do not use, they were mistaken

> each color of light travels at a different speed?

That is indeed correct when light is not traveling through a vacuum. Refraction occurs because of a change in velocity between mediums, and the refractive index is wavelength-dependant (dispersive) in many mediums.

thanks all for the pointers: they led me to an explanation from Feynman, which I'd not found before. And hadn’t seen in high school.

https://www.feynmanlectures.caltech.edu/I_31.html

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