The secret is to purchase things built before "optimization" occurs in the design cycle; i.e. before the accountants and managers get a go at it.

indeed! Typical of stings that were built before the disposable era! They were not only built to last, but also to be maintained and repaired.

well, remember to not buy the cheapest tools you can find next time you go shopping

Wow! 48 inches! That is something to do by hand! David will live on for a long time in the mirrors he made! I have aluminised two mirrors that were older than 100 years already!

This is not at all what John described as the process he used to aluminize the mirrors we ground in his class. He describe a process, from what I can recall, where the glass is suspended a certain distance from the source of the machine that shot out the aluminizer like a few electrons thick across the entire surface of the glass. Of course we never got to witness this process, but we did soon receive our perfect reflector mirrors.

Ah, were you a member of the Aluminati?

Glad you enjoyed this video. Yes, there are a total of three aluminising tanks in Sutherland, SALT, 74-inch and 40-inch. This was done on the latter. I also have a video showing the 74-inch's primary mirror being done - see ukposts.info/have/v-deo/oKiTYYGGqJd0uoU.html

Great to hear @ SCAPE0GOAT. Glad you enjoyed it.

I concur with that statement!!! And no annoying commercials!!!

Indeed! It has all to do with "mean free path" to make sure the aluminium does not meat any oxygen molecules on their way to the mirror, resulting in a black coating!

@@SterremanWillie This is indeed not true. As soon as you open the tank, the Al surface comes in contact with oxygen and forms a layer of Al2O3. It does not become black. High vacuum is needed so that the Al atoms go straight to the surface and deposit there. If ANY gas is present, the Al atoms will hit them and lose energy and direction and result in a poor coating that can be peeled off. Because you are using a simple diffusion pump, you will get a pressure of 10-3 mbar (at best) and the mean free path will be around a couple of cms. So each Al atom will hit a couple of O2 molecules on the way but will not lose much energy and the deposit will be good.

@@janami-dharmam I have not had the (bad) experience of a black coating, but I'm told that that is indeed what happens for the reason explained. As you can see at minute 09:50, the final pressure was better than 2 times 10^-5 mbar

@@janami-dharmam " _As soon as you open the tank, the Al surface comes in contact with oxygen and forms a layer of Al2O3. It does not become black._ " Forming thin layer of Al2O3 is completely different from mixing the Al crystal with a huge amount of random oxygene atoms making it barely metallic. A thin layer of insulator is transparent, while strongly irregular crystal structure in a metal increases its resistivity, which reduces reflectivity.

@@PafiTheOne You are right; Why it should become black at all? It becomes black when it does not reflect any of the visible light back to the observer. As you correctly say a thin layer of Al2O3 is transparent and a thick layer of Al2O3 is white for visible wavelengths.

Thanks very much. Yes, there are indeed not many aluminsing videos on UKposts.

Either "40-grit sandpaper" means something else to you than to me, or you are kidding - I suspect the latter!

@@SterremanWillie Lol...great video Willie, I coated my first 3" mirror 40 years ago in a pickle jar with an Edwards diffstack and roughing pump I got from a pix tube rebuilder. Kinda supprised you don't have preheat shutters on the evap coils.

@@sparkyy0007 Interesting! I have physically seen the insides of about half a dozen aluminising tanks in my life and pictures/videos of another half a dozen, but they were all similar to what we use. Tell me more about preheat shutters please?

@@SterremanWillie There will always be some contaminants on anything you put into a vac chamber no matter how careful. Micro-scratches in the Al wire will hide pull die oils that are impossible to remove with anything but heat. Cleaning solvents, even reagent grade are never 100% pure, and anything that doesn't come off at 21 C will out-gas or boil off. These contaminants will boil off (line of sight) onto the substrate just like the Al, and depending on the composition of the contaminants or their decomposition products when heated can cause surface reactions or adhesion problems with the Al coating. All E-Beam evap systems use a mechanical shutter during warmup to prevent these volatiles from reaching the substrate. The volatiles ( usually oils or hydrocarbons, but sometimes organics and dust) come off at a pretty low temperature, usually far below the melt point. E-beam is extensively used in the semiconductor and optics industry where multiple evaporants are utilized in a single session used for multi-layer stacks, and where coating purity is paramount. No tungsten is heated during the process. moorfield.co.uk/knowledge-base/electron-beam-evaporation/ www.nanomaster.com/images/deposition/e-beam/nee4000-dualclosed.jpg Here is K Leskers units, they shutter their heater boats as well. www.lesker.com/newweb/Vacuum_systems/thumbnail/Photo/Photo-SY-NANO36_04-THUMB.jpg As well, with any tungsten filament evaporator, there is always a small amount of (W) boiled off depending on how hot you run the filaments, and this will reduce the reflectivity, W is really black. If there weren't, we would never need to replace the coils.

@@sparkyy0007 Interesting. This problem gets addressed by doing a "melting on" procedure. You may know this, but what you do is to load the coils and close the tank (without any mirrors) and pump to vacuum. Then you fire the coils only to the point where the aluminium hooks "melt on", i.e. form into bubbles on the coils and stop the current. This boils off all the bad stuff you described. You then release the vacuum, load the mirrors and continue the process as in my video. For some reason, our guys dropped this step, so I don't do this any more either.

Bly jy het dit geniet! Dankie vir jou terugvoer.

Thanks. Great to hear you liked it. Sorry about the sound in places, hope the subscripts helped.

The pumping speed of a small turbo pump is way too low for a tank of this size. Go check out how NASA also still use diff-pumps to evacuate their large vessels/chambers.

Great to hear you enjoyed the video. Good luck to anyone trying to set up a plant based on my video. There is an amazing amount of institutional knowledge not shown!

Yeah, that it will be profitable.😂😂😂😂😂😂😂

Thanks, great to hear.

That is a pity! You are welcome to contact me for help, if you ever want to get something going again. We have four aluminising tanks at our observatory, and I got involved at all of them.

Great! Then you must go watch my other videos on how I assemble our CCD cryostats, do leak-testing on them and cool them down with Liquid nitrogen.

Thanks! Glad to hear you enjoy them.

RocKITEman _ 2001 I’m going to look into it on reflection though

Dankie Johann

Ahhaaa! Baie dankie.

Thanks Richard. With Covid and then a severe drought in the Karoo, I have not done any aluminising for a long time, so there is a huge backlog. I'm also retiring in a year's time, so not sure if I will be able to make this up in time.

@Willie Koorts tough times. I have seen the night sky from your great country just once, from Franschoek. I can't imagine what the night sky at sutherland must be like. Maybe one day...

@@richardd5009 as you say, although Franschoek is not bad, Sutherland is something else. Once you are well dark adapted, you can see your own shadow in the Milky Way! I did not think this was possible, until experiencing it myself.

@@SterremanWillie incredible.

Interesting question. The aluminium do actually oxidise quickly, but it hardens the layer and I don't think change the reflectivity much.

yes aluminium oxide is very very hard, commonly used as an abrasive as it is a 9 on the moh's hardness scale. It is also transparent, meaning as soon as the aluminium is oxidized it gets a skin of this tough clear oxide, and it doesn't corrode any further

Thank for the comment. Our system is not equipped to apply any overcoat unfortunately. I think it is also done under vacuum, but not sure, sorry.

@@SterremanWillie So, what is the average lifespan of an aluminum coating without SIO overcoat ?

Glad you liked the video.

Is that chromium oxide liquid ?

Dankie Danie