I wasn't expecting to see Dernocua at the top of HN today with 53 comments. You can download Dernocua as a whole from http://canonical.org/~kragen/dernocua/ if you're interested.
I'm happy to answer any questions. (Well, almost any.)
Aluminium is usually "good enough" relative to copper on both types of conductivity, it actually beats copper in terms of conductivity per unit weight (which is the factor of interest in many applications) and presumably in terms of material cost too.
This made me wonder about a 3D printer alternative that builds things by folding a thin sheet of metal into arbitrary shapes instead of extruding filament.
I made an artwork in 2013-ish, where I attached an aluminum foil to a good DC motor. I mounted it from the ceiling with 2 stepper motors to control height and one orthogonal axis. The motor would unwind the foil by accelerating quickly in either direction (CW/CCW). By changing directions it would also create folds and stabilize the emerging shape: https://imgur.com/a/gaRKGtQ
I always imagined an additional stepper motor to cover an area like a delta 3D printer and liked to think about the difficulty in creating the 3D software, and the need to find a solution to simulate the unwinding-into-shape through some physical model.
My college had a 'rapid prototyping' machine circa 2000 that worked in paper. Roll out a layer of paper, cut through the top layer, something something glue, roll out the next layer, etc. No reason that couldn't work with aluminum foil.
I can just tell you from experience that aluminum foil is much more fragile than paper, your college might face some difficult challenges in making it work and need to rework their machine. Maybe very lightweight paper comes close, but certainly not the standard 80gsm printing paper.
I created an embossing machine than would emboss aluminum foil with the scratch marks of a teaspoon. Aluminum foil tends to get a fold rather quickly, doing that for 40m was quite a challenge.
I mean, one of the most useful metal fabrication techniques is already folding thin sheets of metal; I learned it in shop class decades ago and it's still a very relevant skill. Some fun stuff here: https://www.youtube.com/watch?v=dS5kwdaNhZo
I appreciated the paean to aluminum foil in Project Hail Mary where (spoilers) the hero uses it as bowling pins and to reproduce astrophage to eventually save two worlds. It's right up there in the pantheon of useful things with duct tape.
> 50¢/m² is 50¢/kWp in a solar concentrator, or 0.05¢/Wp, which is noticeably cheaper than photovoltaic cells, currently around 18¢/Wp, 360 times more expensive.
A photovoltaic cell is a solar panel, and a piece of aluminium does nothing, am I missing something here?
I think the implication is you can use it to reflect additional light onto your photocell, improving the power output for a smaller cost than purchasing an additional cell.
At my previous job we made >1m wide 8um thick copper foil by electroplating it onto a giant titanium drum from blue copper sulfate solution. It was quite impressive.
>Alternatively, though, it might be possible to stiffen the foil by making the equivalent of corrugated cardboard out of it, maybe using aqueous boric acid (US$1.70/kg according to Potential local sources and prices of refractory materials) or borax as the glue. The surface tension of water is ample to hold aluminum foil in place until the water dries.
Hello Amazon? Billion dollar idea here. This needs more attention. You could have fully recyclable aluminum boxes instead of cardboard. Imagine your box supply chain literally being a circle.
aluminum foil is generally not something you can recycle. Not that it can't be recyled, but the oxide to pure aluminum ratio is high and so you don't gain much since you need all the energy of refining in the first place to get back to something usable.
Amazon needs stronger boxes than foil anyway. Cardboard is likely best for them.
Photographers and cinematographers are like: ohhh let me sit you down and tell you all about my love of blackwrap.
Aluminium foil is amazing stuff. Aluminium foil adhesive tape, in particular, is incredibly useful.
Being a multi-domain kind of geek the random tapes section of my tool drawers also contains mylar tape and fashion tape (or "tit tape" as a friend calls it) but the aluminium foil tape has proved to have many useful applications.
It's non-toxic and food safe, and yet a significant number of people on the internet still act like it's poison that will give you Alzheimer's. I wonder how many of those people touch their lips to the lid of an aluminum beverage can. Or how they might bake a lasagna at home.
Let's see if this is a quantitatively plausible concern.
https://en.wikipedia.org/wiki/Aluminium_chloride says orl-rat LD₅₀ of AlCl₃ is 380mg/kg, which is 20.2% aluminum by weight, so that's 77mg/kg of soluble aluminum ions. If this toxicity is due to soluble aluminum ions (rather than, say, acidity), and rats and humans are about equally sensitive to aluminum toxicity, you'd need about 3.8g of aluminum to kill a 50kg human, the ionized equivalent of 1.42mℓ of aluminum metal (at 2.71g/cc). That's 1420cm² of 10μm aluminum foil completely dissolved in the food.
Presumably you would get significant toxic effects well before reaching the lethal dose, so it would be wise to avoid exposures larger than a few tens of cm² of aluminum foil completely dissolved in your food. So it seems like the concern at least passes the first smoke test of plausibility: the total amount of aluminum present in a "grilling packet" is at least sufficient to worry about.
(Fortunately, aluminum rapidly becomes inert in the body, so we don't have to be concerned about gradual poisoning the way we do with lead and arsenic.)
The crucial question, then, is how fast the foil corrodes under cooking conditions! If it corrodes (and migrates into the food) at a micron or more per hour, then this could be a serious concern. But, if the corrosion rate is more like microns per month or microns per year, the dose wouldn't be high enough to worry about.
I put aluminium foil over a bowl of pizza dough, as it grew the top touched the foil and in a few spots tiny holes appeared in the foil. I wonder if it was carbonic acid or what
i heard aluminum food containers are often coated with toxic liners, like plastics, bpa, and pfas.
If Alzheimers isnt a risk with pure aluminum metal, id say those liners are a huge risk.
Are kitchen foils coated? Im pretty sure cans are most of the time.
"Plastic" in general isn't toxic as a liner. It's used in plumbing, and in zillions of containers for potable water and foods. When you get food from even a nice restaurant, they probably marinate meat in a plastic container, and squeeze fruit juice into a plastic container. They sous vide items in plastic.
I've also never heard of a plastic/Alzheimer's connection, only one claimed with aluminum.
i didnt mean those contaminents cause Alzheimers, just that its a risk to general health. food grade plastic is not considered toxic at these doses, but u def dont want it in your body if u can avoid it within reasonable effort.
i use freezer bags made from plastic , and reuse plastic ziplocs from some food stuffs i buy to marinate meat, its really convenient to be able to remove the air and have the marinade fully coat the food.
i reuse plastic water bottles until i forget them somewhere.
im def using plastic to store food.
i eat canned food too, and most of the cans mention something about their liner safety right on the can. bpa-ni is interesting, in that they say they dont intentionally use bpa liner, but bpa could still be there, wtf , how are u so unsure as a manufacturer to what ur inputs are on a factory made can.
that being said, im not storing food in there for years, only hours when i use plastic in my own processes.
plastic in can liners often holds food for years, and the expiration date of canned food is often many years after the food is manufactured and canned.
I just skimmed and read parts but I really enjoyed reading this. It's like my own handwritten notes which are just stray thoughts about a subject. Maybe I should publish more of those and I love the idea of just musing about a single thing, like Aluminum Foil (though it's very interesting stuff).
>Robert Lang recommends laminating tissue paper on one or both sides of kitchen aluminum foil to make “tissue foil”, which for years he considered the ideal origami material.
The sculptor Kim Beaton likes to champion foil as a "metal clay" for sculpting. Keep it full of air pockets and it's easy to shape. You can use hot glue to put parts together, and then cover it in other clays for fine details and coloring. She does quick demos for tour groups at Weta Workshop in New Zealand.
I was enjoying the ADHD hyper focus writing, kind of following along, then:
> If we figure that the foil can meaningfully change direction every 20 μm, then we might think of an aluminum-foil machine as being made of “moving parts” on the order of 1000 μm² (50 μm × 20 μm), 1000 “parts” per square millimeter of foil; a roll of kitchen aluminum foil is enough to fabricate some 4 billion “parts”. A bootstrapping compiler might require 100 000 parts and thus a square centimeter of aluminum foil, cut and folded around into a shape a couple of millimeters in diameter. If it were doing only one thing at a time, and needed 10 seconds to construct/assemble each moving part, it would take about 12 days to recompile itself. This is probably adequately fast, barely, but probably not adequately robust against errors. It would probably be better to design it to have more parts and do many things at once, enabling it to be faster and correct errors.
Um, what? I'd like to see a sketch of this 100,000 part compiler very much. I have no idea what he/she is talking about here, in the slightest. But I am intrigued!
I've read a lot of his other writings so that context might be informing my reading here but it sounds like he's pretty straightforwardly discussing the potential of aluminum foil as a uniform-feedstock-slash-construction-material for a hypothetical self-reproducing microfabricator.
I do not currently have a sketch of a matter compiler, just a rough estimate that most of its parts count would probably be RAM, and that it probably needs several kilobytes of RAM.
It reads like a rambling of a mad scientist, but I think simply adding pictures would make this feel absolutely normal (in the crowd of other blogs featured on hn)
Another thing not mentioned on there about aluminium foil is how clean it is. We work with a laminar flow hood and pull a fresh layer of foil anytime we are working to create a clean base to work on. I can guarantee you that if you run a swab over a fresh sheet of foil and smear it onto sterile nutrient agar that it won't grow anything - that said, we use costco foil which is thicker gauge and not the budget thinner stuff which is definitely inferior.
any tips on how to reliably get that "thicker gauge" one? I've been craving it since maybe 20y ago when I got a roll from my old stint in a restaurant. I've tried buying some rolls by "heavy duty" labels and these days it's just as likely to be one of those thin "look at it funny and it tears".
Costco sell two different types of foil, one is shorter and has blue packaging and the other is longer and has red packaging... It's the red one which is much thicker.
Aluminum is honestly a miracle material that has no business being as inexpensive as it is (of course, this is only since the invention of the Hall–Héroult process, before which aluminum was one of the most expensive metals known despite making up ~8% of the crust).
This is pretty much just rambling about how amazing aluminium foil is because it's so thin and that might enable all sorts of wonderful imaginary applications. Very HN. It's aluminium foil.
That's the neat part though, isn't it? It's a product that's so good that there's no everyday alternatives to it. I was researching cat litter options recently and cat owners do a lot of thinking and talking about litter, because there's a variety of different materials, none of which are solidly better than all others in all situations. But aluminium foil is so good that we don't even think about it, because it's by far the best product for every application that we use it for.
When exposed to air at room temperature, or any other gas containing oxygen, pure aluminium self-passivates by forming a surface layer of amorphous aluminium oxide 2 to 3 nm thick,[4] which provides very effective protection against corrosion. Aluminium alloys typically form a thicker oxide layer, 5–15 nm thick, but tend to be more susceptible to corrosion.
Has a kid, my mom used to pack my lunch in aluminium foil and everyday was a challenge of trying to make the perfect aluminium ball and throw it in the trashcan[1] on the first try!
Read this guy's ramblings and give me one cool application that he has found. Lots of "maybe it could do this!" and "it can do <completely useless thing>!"
The trick to being a good hacker is acquiring a sufficient supply of useless information, such that when that information is suddenly not useless, you have it at hand.
Which is to say, it's your job to figure out what the cool applications are.
Aluminum foil makes a great, cheap light bounce for photography on the fly. Your photos will instantly look better either reflecting to the back of their head 180 from shot, or as a fill for their face.
I wasn't expecting to see Dernocua at the top of HN today with 53 comments. You can download Dernocua as a whole from http://canonical.org/~kragen/dernocua/ if you're interested.
I'm happy to answer any questions. (Well, almost any.)
What's up with the dercuano, derctuo, and dernocua naming? Are there just these three? Does the naming follow some pattern?
seems like the cert may have expired
Thanks! I keep unintentionally using https links to canonical.org since basically the whole web is https now. Fixed.
>...and conductive, rivaling copper.
That isn't true for either thermal or electrical conductivity. So I don't know what is meant here.
Aluminium is usually "good enough" relative to copper on both types of conductivity, it actually beats copper in terms of conductivity per unit weight (which is the factor of interest in many applications) and presumably in terms of material cost too.
This made me wonder about a 3D printer alternative that builds things by folding a thin sheet of metal into arbitrary shapes instead of extruding filament.
I made an artwork in 2013-ish, where I attached an aluminum foil to a good DC motor. I mounted it from the ceiling with 2 stepper motors to control height and one orthogonal axis. The motor would unwind the foil by accelerating quickly in either direction (CW/CCW). By changing directions it would also create folds and stabilize the emerging shape: https://imgur.com/a/gaRKGtQ
I always imagined an additional stepper motor to cover an area like a delta 3D printer and liked to think about the difficulty in creating the 3D software, and the need to find a solution to simulate the unwinding-into-shape through some physical model.
EDIT: unwinding GIF here: https://imgur.com/a/VP3gEiv
Imgur is not working anymore in UK :(
Alternative links:
https://postimg.cc/Q9vjhdrk
https://postimg.cc/9D1Vzphj
My college had a 'rapid prototyping' machine circa 2000 that worked in paper. Roll out a layer of paper, cut through the top layer, something something glue, roll out the next layer, etc. No reason that couldn't work with aluminum foil.
I can just tell you from experience that aluminum foil is much more fragile than paper, your college might face some difficult challenges in making it work and need to rework their machine. Maybe very lightweight paper comes close, but certainly not the standard 80gsm printing paper.
I created an embossing machine than would emboss aluminum foil with the scratch marks of a teaspoon. Aluminum foil tends to get a fold rather quickly, doing that for 40m was quite a challenge.
The embossing machine: https://postimg.cc/67wkVGBy
The embossing process as GIF: https://postimg.cc/3W6zSqKx
The embossed aluminum foil as GIF: https://postimg.cc/yDh5NY0D
This is very impressive!
I mean, one of the most useful metal fabrication techniques is already folding thin sheets of metal; I learned it in shop class decades ago and it's still a very relevant skill. Some fun stuff here: https://www.youtube.com/watch?v=dS5kwdaNhZo
They do this. This is the coolest one IMO:
https://mantle3d.com/
That's not how mantle3d works. It's 3d printed metal alternating with CNC machining after several layers for precision:
https://mantle3d.com/how-it-works/
This is optionally followed by a pressurized furnace for sintering.
I appreciated the paean to aluminum foil in Project Hail Mary where (spoilers) the hero uses it as bowling pins and to reproduce astrophage to eventually save two worlds. It's right up there in the pantheon of useful things with duct tape.
> 50¢/m² is 50¢/kWp in a solar concentrator, or 0.05¢/Wp, which is noticeably cheaper than photovoltaic cells, currently around 18¢/Wp, 360 times more expensive.
A photovoltaic cell is a solar panel, and a piece of aluminium does nothing, am I missing something here?
https://en.wikipedia.org/wiki/Concentrated_solar_power
I think the implication is you can use it to reflect additional light onto your photocell, improving the power output for a smaller cost than purchasing an additional cell.
This was on S01E01 of How It's Made. Probably one of the best segments in the shows history.
At my previous job we made >1m wide 8um thick copper foil by electroplating it onto a giant titanium drum from blue copper sulfate solution. It was quite impressive.
>Alternatively, though, it might be possible to stiffen the foil by making the equivalent of corrugated cardboard out of it, maybe using aqueous boric acid (US$1.70/kg according to Potential local sources and prices of refractory materials) or borax as the glue. The surface tension of water is ample to hold aluminum foil in place until the water dries.
Hello Amazon? Billion dollar idea here. This needs more attention. You could have fully recyclable aluminum boxes instead of cardboard. Imagine your box supply chain literally being a circle.
I don't know about corrugated aluminium, but aluminium honeycomb is definitely a thing: https://www.easycomposites.co.uk/aluminium-honeycomb
That would be hell on everybody's box-cutters (and fingers). I already cut myself too often on shipping boxes.
Cardboard is very recyclable already.
aluminum foil is generally not something you can recycle. Not that it can't be recyled, but the oxide to pure aluminum ratio is high and so you don't gain much since you need all the energy of refining in the first place to get back to something usable.
Amazon needs stronger boxes than foil anyway. Cardboard is likely best for them.
the oxide to pure aluminum ratio is high
For some definition of high? Standard foil is around 20 um thick while the oxide layer only goes about 10 nm deep.
Photographers and cinematographers are like: ohhh let me sit you down and tell you all about my love of blackwrap.
Aluminium foil is amazing stuff. Aluminium foil adhesive tape, in particular, is incredibly useful.
Being a multi-domain kind of geek the random tapes section of my tool drawers also contains mylar tape and fashion tape (or "tit tape" as a friend calls it) but the aluminium foil tape has proved to have many useful applications.
Such as?
It's non-toxic and food safe, and yet a significant number of people on the internet still act like it's poison that will give you Alzheimer's. I wonder how many of those people touch their lips to the lid of an aluminum beverage can. Or how they might bake a lasagna at home.
You shouldn't use aluminum foil with tomato/lemon/vinegar/brined foods or as "grilling packets" (direct fire/high heat) because of leaching risk.
There's no concern with using aluminum in most cases (with dry/non-acidic foods) but leaching is a real problem with acidic/salty/wet/high eat.
Let's see if this is a quantitatively plausible concern.
https://en.wikipedia.org/wiki/Aluminium_chloride says orl-rat LD₅₀ of AlCl₃ is 380mg/kg, which is 20.2% aluminum by weight, so that's 77mg/kg of soluble aluminum ions. If this toxicity is due to soluble aluminum ions (rather than, say, acidity), and rats and humans are about equally sensitive to aluminum toxicity, you'd need about 3.8g of aluminum to kill a 50kg human, the ionized equivalent of 1.42mℓ of aluminum metal (at 2.71g/cc). That's 1420cm² of 10μm aluminum foil completely dissolved in the food.
Presumably you would get significant toxic effects well before reaching the lethal dose, so it would be wise to avoid exposures larger than a few tens of cm² of aluminum foil completely dissolved in your food. So it seems like the concern at least passes the first smoke test of plausibility: the total amount of aluminum present in a "grilling packet" is at least sufficient to worry about.
(Fortunately, aluminum rapidly becomes inert in the body, so we don't have to be concerned about gradual poisoning the way we do with lead and arsenic.)
The crucial question, then, is how fast the foil corrodes under cooking conditions! If it corrodes (and migrates into the food) at a micron or more per hour, then this could be a serious concern. But, if the corrosion rate is more like microns per month or microns per year, the dose wouldn't be high enough to worry about.
What is the leaching risk, though? If aluminum does get in your food, is it bad for you in a specific way, or is it more like iron?
I put aluminium foil over a bowl of pizza dough, as it grew the top touched the foil and in a few spots tiny holes appeared in the foil. I wonder if it was carbonic acid or what
i heard aluminum food containers are often coated with toxic liners, like plastics, bpa, and pfas. If Alzheimers isnt a risk with pure aluminum metal, id say those liners are a huge risk. Are kitchen foils coated? Im pretty sure cans are most of the time.
"Plastic" in general isn't toxic as a liner. It's used in plumbing, and in zillions of containers for potable water and foods. When you get food from even a nice restaurant, they probably marinate meat in a plastic container, and squeeze fruit juice into a plastic container. They sous vide items in plastic.
I've also never heard of a plastic/Alzheimer's connection, only one claimed with aluminum.
i didnt mean those contaminents cause Alzheimers, just that its a risk to general health. food grade plastic is not considered toxic at these doses, but u def dont want it in your body if u can avoid it within reasonable effort. i use freezer bags made from plastic , and reuse plastic ziplocs from some food stuffs i buy to marinate meat, its really convenient to be able to remove the air and have the marinade fully coat the food. i reuse plastic water bottles until i forget them somewhere. im def using plastic to store food. i eat canned food too, and most of the cans mention something about their liner safety right on the can. bpa-ni is interesting, in that they say they dont intentionally use bpa liner, but bpa could still be there, wtf , how are u so unsure as a manufacturer to what ur inputs are on a factory made can. that being said, im not storing food in there for years, only hours when i use plastic in my own processes. plastic in can liners often holds food for years, and the expiration date of canned food is often many years after the food is manufactured and canned.
I've only seen people concerned with it in antiperspirants, where it's a salt. (And to be clear, I think it's BS.)
As with NaCl, it's at least possible that the salt and the pure-ish variant aren't quite the same thing.
1) all of them
2) glass dish
I use a glass/Pyrex dish, but put foil on top. I guess you could use a fitted glass lid instead, depending on the container.
I just skimmed and read parts but I really enjoyed reading this. It's like my own handwritten notes which are just stray thoughts about a subject. Maybe I should publish more of those and I love the idea of just musing about a single thing, like Aluminum Foil (though it's very interesting stuff).
>Robert Lang recommends laminating tissue paper on one or both sides of kitchen aluminum foil to make “tissue foil”, which for years he considered the ideal origami material.
The sculptor Kim Beaton likes to champion foil as a "metal clay" for sculpting. Keep it full of air pockets and it's easy to shape. You can use hot glue to put parts together, and then cover it in other clays for fine details and coloring. She does quick demos for tour groups at Weta Workshop in New Zealand.
I was enjoying the ADHD hyper focus writing, kind of following along, then:
Um, what? I'd like to see a sketch of this 100,000 part compiler very much. I have no idea what he/she is talking about here, in the slightest. But I am intrigued!I've read a lot of his other writings so that context might be informing my reading here but it sounds like he's pretty straightforwardly discussing the potential of aluminum foil as a uniform-feedstock-slash-construction-material for a hypothetical self-reproducing microfabricator.
I do not currently have a sketch of a matter compiler, just a rough estimate that most of its parts count would probably be RAM, and that it probably needs several kilobytes of RAM.
It reads like a rambling of a mad scientist, but I think simply adding pictures would make this feel absolutely normal (in the crowd of other blogs featured on hn)
Another thing not mentioned on there about aluminium foil is how clean it is. We work with a laminar flow hood and pull a fresh layer of foil anytime we are working to create a clean base to work on. I can guarantee you that if you run a swab over a fresh sheet of foil and smear it onto sterile nutrient agar that it won't grow anything - that said, we use costco foil which is thicker gauge and not the budget thinner stuff which is definitely inferior.
Wasn't it a think that "stuff" dies on exposed metal?
any tips on how to reliably get that "thicker gauge" one? I've been craving it since maybe 20y ago when I got a roll from my old stint in a restaurant. I've tried buying some rolls by "heavy duty" labels and these days it's just as likely to be one of those thin "look at it funny and it tears".
Costco sell two different types of foil, one is shorter and has blue packaging and the other is longer and has red packaging... It's the red one which is much thicker.
I had no idea about that!
Worth noting that aluminum is the most abundant metal of the Moon’s highland geography, thus excellent for bootstrapping beyond Earth.
Aluminum is honestly a miracle material that has no business being as inexpensive as it is (of course, this is only since the invention of the Hall–Héroult process, before which aluminum was one of the most expensive metals known despite making up ~8% of the crust).
Yup. The very tip of the Washington Monument was made of aluminium, which made it faaaaaancy. Two years later, not so much.
Amazing. This reads like someone left Hunter S. Thompson alone with a roll of Reynolds Wrap.
Thank you.
Im interested in using honeycomb aluminum panels for some projects but curious why its so freaking expensive?
There's even a song about it:
https://youtube.com/watch?v=urglg3WimHA
This is pretty much just rambling about how amazing aluminium foil is because it's so thin and that might enable all sorts of wonderful imaginary applications. Very HN. It's aluminium foil.
That's the neat part though, isn't it? It's a product that's so good that there's no everyday alternatives to it. I was researching cat litter options recently and cat owners do a lot of thinking and talking about litter, because there's a variety of different materials, none of which are solidly better than all others in all situations. But aluminium foil is so good that we don't even think about it, because it's by far the best product for every application that we use it for.
What's really thin is the oxide layer on the surface
https://en.wikipedia.org/wiki/Anodizing
When exposed to air at room temperature, or any other gas containing oxygen, pure aluminium self-passivates by forming a surface layer of amorphous aluminium oxide 2 to 3 nm thick,[4] which provides very effective protection against corrosion. Aluminium alloys typically form a thicker oxide layer, 5–15 nm thick, but tend to be more susceptible to corrosion.
it usually is not only aluminium oxide but a mixture of aluminium oxide and aluminium hydroxide if it is normal (read: moist) air
You sound like someone who hasn't explored the upper limits of what aluminum foil can solve!
Has a kid, my mom used to pack my lunch in aluminium foil and everyday was a challenge of trying to make the perfect aluminium ball and throw it in the trashcan[1] on the first try!
1. Recycling was a vague concept in the 80s & 90s
Your local recycler probably doesn't want al foil even today when recycling is a big thing.
Read this guy's ramblings and give me one cool application that he has found. Lots of "maybe it could do this!" and "it can do <completely useless thing>!"
The trick to being a good hacker is acquiring a sufficient supply of useless information, such that when that information is suddenly not useless, you have it at hand.
Which is to say, it's your job to figure out what the cool applications are.
Aluminum foil makes a great, cheap light bounce for photography on the fly. Your photos will instantly look better either reflecting to the back of their head 180 from shot, or as a fill for their face.