Contents:
0:00 Intro
1:00 On the risks of Hydrofluoric Acid
4:56 Buffered Oxide Etch (BOE)
6:06 Glass protection with Photoresist
7:17 Glass protection with Chromium
9:12 Laser Induced Etching (LIE, LIDE)
12:20 Smallest Tesla valves in the World. No, Universe! (As far as I can tell).

This video contains an overview of some glass etching experiments I did with Buffered Oxide Etch (HF / NH4F). Just for the record: the video is not meant as an encouragement to start experimenting with concentrated HF yourself. If the info in this video did not scare you off, please study the following webpage before proceeding. (Warning: page contains unpleasant graphics):
https://www.emsworld.com/article/1733...

The video contains some images and clips taken from third party webpages and other Youtube channels. Please visit these to refer to the original content by clicking the links below. Did I forget anything? please let me know and I will set it straight.

functions of calcium in cells:
https://www.cell.com/fulltext/S0092-8...

function of Calcium in the nerve system:
https://basicmedicalkey.com/introduct...

Images of Crystal structures:
http://www.quartzpage.de/
https://www.britannica.com/topic/glas...

The delivery guy was taken from :
https://www.freepik.com/

I deliberately did not discuss the way Tesla valves work, but these videos do (or demo its principle, short clips were used):
NightHawkInLight:    • Tesla Valve Explained With Fire  
The Thought Emporium:    • Worlds Smallest Tesla Valve? - Shrink...  
The Action Lab:    • This Tesla Valve Straw Only Works In ...  
Kasper Keizer:    • Large scale Tesla valve (1 meter) wit...  
Integza:    • Tesla Valve 3D Printed  

In the video I made referrals to Lightfab and LPKF / Vitrion. I do not have any commercial ties with these companies. If the part on "laser induced etching" got you interested in their products, please visit their respective websites:
https://lightfab.de/
https://www.lpkf.com/en/industries-te...
https://www.vitrion.com/en/lide-techn...

a small clip of the following lightfab video was used:
   • LightFabbing3D of a planetary drive  

For an overview of AZ-photoresists you can refer to the following page:
https://www.microchemicals.com/produc...

The article below contains some good information on surface roughness introduced by etching
https://www.osapublishing.org/oe/full...