Costa Rica's Turquoise River - A Natural Optical Illusion

That blue water doesn't look too natural to me.

I mean it's a gorgeous blue, but it's a blue that doesn't seem quite right.

Apparently - at least according to this article - there's no copper in the water, so that's not what it's blue.

Instead, the Rio Celeste produces particulates of aluimosilicate of exactly the right size to reflect light in the blue area of the spectrum. Neither tributary contains particles of the right size, but...

[t]here was only one puzzle left to solve, though. If Rio Buena Vista also had an abundance of aluminosilicate, how come its water looked completely transparent, while Rio Celeste appeared to be turquoise? It turned out to be a matter of particle size. Upon analyzing samples from both bodies of water, scientists realized that aluminosilicate particles in Rio Buena Vista measured 184 nanometers (nm), while those in Rio Celeste were much larger at 566 nm

“This increase in size is what causes the scattering of sunlight, such that it occurs principally in the blue region of the visible spectrum. So that’s why we have that spectacular light blue color of the Rio Celeste” said Dr. Max Chavarría Vargas, who lead the scientific investigation into the turquoise waters of Rio Celeste. “It’s one of those quirks of nature where one of the rivers provides mineral material with one size and the other river provides the acidic environment so that those particles grow.”

Who knew that particulate size mattered?

Brad Makes a Knife with Bob Kramer | It's Alive | Bon Appétit

I'm a fan of goofy Brad, the host of the video series, It's Alive. Mostly the show is about cooking in the realm of fermented foods (kombucha, beer, garlic honey, cultured butter, sauerkraut, etc), but this time Brad goes to a small-scale knife shop because, as he says at about 13:10, "this ain't necessarily alive, but it's got energy...watching [the knife-making process] from start to finish, if it don't make you feel alive, I can't help you.

There are a bunch of metal topics covered here...

• 0:45 - "make some steel from scratch"...they make their steel from powdered ingredients (carbon, iron, manganese) and then melt them together
• 1:30 - induction heat melting of the steel ingredients
• 2:20 (and again at 3:00) - forging...the take the fresh, steel 'biscuit', reheat it 
• 2:45 - heating the steel back up to the plastic state...they don't mention the phase transition from BCC to FCC, but they do explain that hot steel can change it shape more easily...and that they have to reheat the 'biscuit' because it's getting cold
• 3:30 - rolling mill...a small mill but still far larger than what we show in the summer workshop
• 4:15 - forge welding different steels together...they only refer to the steels as steel A and steel B...no mention of high- or low-carbon steels
• 4:40 - iron oxide...the captions explain that, "[t]hose dark flakes are iron oxide. High temperatures accelerate the oxidation process."
• 6:20 - "quench tank there, Vinnie"...Vinnie is the camera man for all the Bon Appétit videos...no explanation yet as to why you would quench something
• 6:58 - hardening the knife...molten salt bath for an oxygen-free atmosphere for heating..."dissolving the carbon into the iron" then capturing it during the quench...followed by a tempering bath to, "bring the knife to a working hardness, so it's not too hard...not too brittle"..."when it's hardened, it's under a lot of STRESS...we go in there (the tempering bath) and it just adds some heat, kind of massages it...makes the knife 'happy'...yeah, this is the 'martini' for the knife"...there's a decent graphic summary of this at 7:50
• 8:40 - acid etching the knife..."the acid eats these layers at a different rate...because we mixed in different things in the steel"
• 11:20 - nothing curricular, but watching Bob Kramer put a blade on the knife just by eye as stunning...I assume it took a few more passes than what the video shows, but he makes it look so casual and awesome...I'm amazed

Warnings

• 7:35 - mention of making the steel happy via a 'martini'
• 10:20 - there's a bleeped, "I always f*#^ that up"

Brad's a goof, but it's loads of fun to watch him make a knife.