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An effective black paint for telescopes

ATM EAA Celestron
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#1 Visit-the-Moon

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Posted 11 July 2020 - 12:45 AM

Recently I found a black acrylic paint with excellent properties. It has a matt finish with very low reflectivity at low incidence angles in red and near-IR light and it is fairly robust, does not mark if touched or scraped and is waterproof. And relatively non-toxic. Maybe not as good as Black 3.0 but I don’t have access to that.

 

French art company Sennelier produce high quality paints that contain very high pigment content. Their Mars Black (Noir de Mars) 759 acrylic paint uses nanoparticle black iron oxide pigment (PBk11). It gives a matt finish and brushes clean up in water. It is sold in a small 60mL (2 fl/oz) plastic bag. One bag was enough for me to paint the inside of two C925s, a dew shield and all the small baffles. I applied the paint with a 12” artist brush, dappling to give a slightly rough finish. It has very nice properties as a paint. It adheres well to painted surfaces (i.e. original black paint), black anodized aluminium and PVC plastic. Raw metal surfaces require a suitable primer, but it can coat un-primed ss bolt heads and nuts. It is very thick and doesn’t run at all. It dries in 30 min, but seems to come to its darkest after a few hours.

 

I used a modified Canon 450D that is sensitive to IR, fitted with an Astronomik 642nm BP filter (band pass 642-840nm), so that I could assess reflectivity at low incidence angles in red and near-IR light, covering wavelengths important for deep-sky, lunar and planetary imaging. Some surprises: the black anodised aluminium used in small adapters etc is highly reflective! Black paper is also not especially good. Regular black paints are not good. Theatre paint is not so good. The original paint finishes in my three Celestrons and my Meade 16” were not especially good. Black velvet is very good. Black sharpie ink is reflective.

 

Looking square on (90 deg), Sennelier’s Mars 759 acrylic black is no better than a typical black paint by eye but at low incidence angle you can see the difference. The IR sensitive camera shows a big difference.

 

The first images (iPhone) of test-painted aluminium blocks are captured outside on an overcast day at 90deg, ~45deg and ~15deg angles on a black cardboard base. You can see the Mars black is superior at low angles. The big surprise is in deep red/near IR. In the final image I half painted a black anodised M42 T-spacer. You can see the anodising is useless.

 

After I painted the inside of my hyperstar CPC 925 (f/2.3), I was surprised that shining a white light torch onto the calibration bolts hence onto the corrector plate (originals replaced by ss allen head bolts) did not wash out the image on camera (red light). EAA at f/2.3 appears to have improved contrast. The inside of the telescope tube certainly looks much darker than with the original paint.

 

Anyway, that is what I found. I don’t like the idea of cementing paper or cork or sawdust or sand, etc into the telescope and I wanted a robust black surface that won’t scuff so I can clean the inside if and when required.

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  • Al blocks IR light_800.jpg
  • Half painted Al spacer_800.jpg

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#2 Oberon

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Posted 11 July 2020 - 01:11 AM

Nice work! waytogo.gif



#3 futuneral

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Posted 11 July 2020 - 02:08 AM

Excellent! Thanks for the tip.

 

When you have a minute and spare two bucks, it'd be nice to see some pictures from your IR rig of this fine specimen:

 

https://www.michaels...2/10218644.html

 

I wonder how it would compare to the paint. I used this paper for flocking a few times and even though it was a bit worse than the ScopeStuff stuff, it was pretty close.


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#4 Supernova74

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Posted 11 July 2020 - 08:38 AM

hi I really understand what your trying to achieve ie flocking the inside of a sct cassagrain is an open debate there and also scrutiny it actually works in first place as there is no facts and figures to go by would it be worth dismantling an sct correcter plate without knowing any optical gain has been achieved I would say no.and feel the only way you will find out in the long term is to have two identical scopes side by side with each other one with flocking material or painted and one without.

thats not saying it will not work with other telescope optical designs.

where flocking can be definitely improved is on the internal OTA baffle by just painting the outside edge approximately 2” in something you have used with non reflective Matt black paint.

the reason for this is not so much to iliminate the OTA reflective surface but baffle can cause halo anomaly’s around very bright stars ie Vega and has been known to show up in both brands from celestron and Meade.



#5 don clement

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Posted 11 July 2020 - 11:43 AM

To enhance the effectiveness of the black paint I use geometry. For example I would  use sharp V threads on the ID of a tube. Like to see results similar to what was done to the black paint with geometry added.

 

Don


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#6 Oregon-raybender

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Posted 11 July 2020 - 02:04 PM

Here is the results I posted in a early inquest on the subject, tested at optics lab.

Yes, black anodize does reflect strongly in the NIR, starting at ~850nm.

Krylon Flat Black seems to work best.

 

Here is the best reference professional paper I could find on the subject.

 

This should answer most ATMers questions about blacking materials.

 

https://arxiv.org/ft...7/1407.8265.pdf

 

Starry Nightswaytogo.gif

 

 

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#7 stargazer193857

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Posted 11 July 2020 - 04:52 PM

Here is the results I posted in a early inquest on the subject, tested at optics lab.

Yes, black anodize does reflect strongly in the NIR, starting at ~850nm.

Krylon Flat Black seems to work best.

 

Here is the best reference professional paper I could find on the subject.

 

This should answer most ATMers questions about blacking materials.

 

https://arxiv.org/ft...7/1407.8265.pdf

 

Starry Nightswaytogo.gif

From that graph, krylon seems good enough that I'd go for the low priced or longer lasting paint.



#8 stargazer193857

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Posted 11 July 2020 - 04:55 PM

Recently I found a black acrylic paint with excellent properties. It has a matt finish with very low reflectivity at low incidence angles in red and near-IR light and it is fairly robust, does not mark if touched or scraped and is waterproof. And relatively non-toxic. Maybe not as good as Black 3.0 but I don’t have access to that.

 

French art company Sennelier produce high quality paints that contain very high pigment content. Their Mars Black (Noir de Mars) 759 acrylic paint uses nanoparticle black iron oxide pigment (PBk11). It gives a matt finish and brushes clean up in water. It is sold in a small 60mL (2 fl/oz) plastic bag. One bag was enough for me to paint the inside of two C925s, a dew shield and all the small baffles. I applied the paint with a 12” artist brush, dappling to give a slightly rough finish. It has very nice properties as a paint. It adheres well to painted surfaces (i.e. original black paint), black anodized aluminium and PVC plastic. Raw metal surfaces require a suitable primer, but it can coat un-primed ss bolt heads and nuts. It is very thick and doesn’t run at all. It dries in 30 min, but seems to come to its darkest after a few hours.

 

I used a modified Canon 450D that is sensitive to IR, fitted with an Astronomik 642nm BP filter (band pass 642-840nm), so that I could assess reflectivity at low incidence angles in red and near-IR light, covering wavelengths important for deep-sky, lunar and planetary imaging. Some surprises: the black anodised aluminium used in small adapters etc is highly reflective! Black paper is also not especially good. Regular black paints are not good. Theatre paint is not so good. The original paint finishes in my three Celestrons and my Meade 16” were not especially good. Black velvet is very good. Black sharpie ink is reflective.

 

Looking square on (90 deg), Sennelier’s Mars 759 acrylic black is no better than a typical black paint by eye but at low incidence angle you can see the difference. The IR sensitive camera shows a big difference.

 

The first images (iPhone) of test-painted aluminium blocks are captured outside on an overcast day at 90deg, ~45deg and ~15deg angles on a black cardboard base. You can see the Mars black is superior at low angles. The big surprise is in deep red/near IR. In the final image I half painted a black anodised M42 T-spacer. You can see the anodising is useless.

 

After I painted the inside of my hyperstar CPC 925 (f/2.3), I was surprised that shining a white light torch onto the calibration bolts hence onto the corrector plate (originals replaced by ss allen head bolts) did not wash out the image on camera (red light). EAA at f/2.3 appears to have improved contrast. The inside of the telescope tube certainly looks much darker than with the original paint.

 

Anyway, that is what I found. I don’t like the idea of cementing paper or cork or sawdust or sand, etc into the telescope and I wanted a robust black surface that won’t scuff so I can clean the inside if and when required.

Where do we buy it?

Is primer needed for aluminum?

 

Sounds like it would go great on a spider. I just worry about thickness. So would other paint though. I wonder how much thin rough powder coat costs, and how effective. 

 

On a spider, radial brush marks are good.



#9 Steve Dodds

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Posted 11 July 2020 - 05:14 PM

A while ago there was a thread on black 3.0 that showed is was as black as could be when put on and wet, but once dried was pretty gray, they said Krylon was blacker when dry.


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#10 MitchAlsup

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Posted 11 July 2020 - 05:29 PM

To enhance the effectiveness of the black paint I use geometry. 

The old sawdust trick is also a geometric trick!

 

Pain the inside of the tube with some kind of glue, dump in quarts of sawdust, tamp sawdust into glue, let dry, and shake out excess sawdust. Then paint with the flattest black spray you can access.

 

The sawdust created millions upon millions of tiny little baffles and traps. And is, in effect, a greatly scaled up version of what flat black paint tries to be -- rough.


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#11 macleod

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Posted 11 July 2020 - 05:45 PM

visit-the-moon - Sennelier seem to be an ARTISTS PAINT producer specialising in oil paints with a high pigment content , and hardness. Some artists supplies shops here in NZ supply these paints. Macleod



#12 Visit-the-Moon

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Posted 11 July 2020 - 06:21 PM

Macleod, Yes, the paint was developed for artists, it is sold by quality art suppliers globally. You won't find it in the hardware store. Important point: this is a water-based acrylic paint. Don't use any oil-based paints, they are very very slow drying & are typically based on linseed oil (or similar oil) & turpentine. Here is an image of the 60 mL pack. It costs A$7.50 per pack, no doubt less in USA & Europe. It is also available in larger pack sizes.

 

It is so cheap. For anyone interested buy some, give it a try on some test materials, if it doesn't work to your satisfaction, don't use it.

 

Incidentally Sennelier has a strong technical background. They invented & developed the oil pastel medium with Pablo Picasso in 1948-1950. Most recently they have developed materials for other major artists including David Hockney, considered by many to be one of the greatest living painters. Of course their paints weren't developed for astronomy!

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#13 Visit-the-Moon

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Posted 11 July 2020 - 06:49 PM

Stargazer193857 - I found the paint bonded well to anodised aluminium. It can bond to raw aluminium, but certainly better to a surface coated with spray-based metal primer. The paint spreads well & can be applied to give a thin coat - have a look at the image of the part-painted spacer I posted earlier. It is not a thick, gluggy, lumpy paint. I have used powder coating before - this is a much thinner coat than powder coating. I'll do a before & after micrometer measurement, let's see. I think the performance is in low angle light incidence situations, such as spiders, telescope tubes & baffles, rather than square on light absorption.



#14 stargazer193857

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Posted 11 July 2020 - 08:41 PM

Recently I found a black acrylic paint with excellent properties. It has a matt finish with very low reflectivity at low incidence angles in red and near-IR light and it is fairly robust, does not mark if touched or scraped and is waterproof. And relatively non-toxic. Maybe not as good as Black 3.0 but I don’t have access to that.

French art company Sennelier produce high quality paints that contain very high pigment content. Their Mars Black (Noir de Mars) 759 acrylic paint uses nanoparticle black iron oxide pigment (PBk11). It gives a matt finish and brushes clean up in water. It is sold in a small 60mL (2 fl/oz) plastic bag. One bag was enough for me to paint the inside of two C925s, a dew shield and all the small baffles. I applied the paint with a 12” artist brush, dappling to give a slightly rough finish. It has very nice properties as a paint. It adheres well to painted surfaces (i.e. original black paint), black anodized aluminium and PVC plastic. Raw metal surfaces require a suitable primer, but it can coat un-primed ss bolt heads and nuts. It is very thick and doesn’t run at all. It dries in 30 min, but seems to come to its darkest after a few hours.

I used a modified Canon 450D that is sensitive to IR, fitted with an Astronomik 642nm BP filter (band pass 642-840nm), so that I could assess reflectivity at low incidence angles in red and near-IR light, covering wavelengths important for deep-sky, lunar and planetary imaging. Some surprises: the black anodised aluminium used in small adapters etc is highly reflective! Black paper is also not especially good. Regular black paints are not good. Theatre paint is not so good. The original paint finishes in my three Celestrons and my Meade 16” were not especially good. Black velvet is very good. Black sharpie ink is reflective.

Looking square on (90 deg), Sennelier’s Mars 759 acrylic black is no better than a typical black paint by eye but at low incidence angle you can see the difference. The IR sensitive camera shows a big difference.

The first images (iPhone) of test-painted aluminium blocks are captured outside on an overcast day at 90deg, ~45deg and ~15deg angles on a black cardboard base. You can see the Mars black is superior at low angles. The big surprise is in deep red/near IR. In the final image I half painted a black anodised M42 T-spacer. You can see the anodising is useless.

After I painted the inside of my hyperstar CPC 925 (f/2.3), I was surprised that shining a white light torch onto the calibration bolts hence onto the corrector plate (originals replaced by ss allen head bolts) did not wash out the image on camera (red light). EAA at f/2.3 appears to have improved contrast. The inside of the telescope tube certainly looks much darker than with the original paint.

Anyway, that is what I found. I don’t like the idea of cementing paper or cork or sawdust or sand, etc into the telescope and I wanted a robust black surface that won’t scuff so I can clean the inside if and when required.


Please take one more picture angle, with the light shining the same direction the camera points, to see how much comes back.

#15 Visit-the-Moon

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Posted 11 July 2020 - 09:22 PM

Oregon-raybender, thanks for posting the reflectivity spectra – exactly the sort of data required in this black coating debate. I assume they are based upon a perpendicular beam with both specular and diffuse reflected light being used to calculate the absorption at a given wavelength.  Have you seen or recorded any information on the performance of these paints at high incidence angles? There must be published information.

 

I had come across the Marshall paper some time ago, just went back & had another look at it. They measured specular (i.e mirror-like) reflectance at 10 deg, 22 deg & 44 deg incidence angles using a helium-neon laser (633nm) but then presented averaged results rather than as a function of incidence angle. They were looking at general performance rather than looking specifically at the performance at glancing light angles typical within a telescope e.g. tube wall, baffle tubes, spider vanes, etc.

 

My bad, the angles given in my original images are wrt the horizontal surface not incidence angle… Incidence angle = (90 deg – stated angle). But you can see the images.


Edited by Visit-the-Moon, 11 July 2020 - 09:24 PM.


#16 stargazer193857

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Posted 11 July 2020 - 10:00 PM

https://www.walmart....500ml/135091632

$21 for 120ml at Walmart.

#17 Visit-the-Moon

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Posted 11 July 2020 - 10:28 PM

Stargazer193857, well there you go, Walmart sells everything!



#18 stargazer193857

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Posted 11 July 2020 - 11:27 PM

I'm reading that primer comes in black, grey, white, and red. So black it would be.

For wood I'm thinking about black stain.

#19 Visit-the-Moon

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Posted 12 July 2020 - 02:35 AM

stargazer193857, sounds like you are going to check it out. The paint was designed to adhere to paper, canvas, wood etc, but for ATM purposes probably best to seal the wood and as you say apply a dark, ideally black primer. It is an expensive paint if you were covering a large surface area - it will go further if the surface is sealed. I have used Sennelier products for art purposes... but I have only looked at ATM application of 759 to metal and plastic surface. All my telescopes are steel or aluminium. It wouldn't matter much whether the primer was a matt or satin finish as long as there is good adhesion. 

 

Mars Black is "opaque" but it is a very slightly transparent black. It sounds counter-intuitive that this would be a good paint for the interior of telescope tubes. However I painted it over existing black surfaces & observed that it was very dark when viewed at a low angle (incidence angle >75 deg) when facing towards the light source. I don't think it is the best paint at all where a square on black is required, say in a cinema room or as an eye-piece baffle shield in an open frame Newtonian. Just like anything you build, a combination of methods is probably best. However, I painted the inside of one of my plastic dew shields, now it looks black. The image below shows photos taken seconds apart of non-painted & painted Celestron dewshields in identical positions (Canon EOS 450D (IR Mod), 24mm lens, f/4.5, 1/10 sec, ISO800, on tripod), late afternoon. The black one is for my hyperstar - the other is just a spare.

 

Dew Shield comparison_2.jpg


Edited by Visit-the-Moon, 12 July 2020 - 06:00 PM.


#20 LU1AR

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Posted 12 July 2020 - 12:55 PM

I used chalkboard paint; added with laser printer toner, with excellent result.
I hope this helps someone.
Regards.
Edgardo



#21 stargazer193857

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Posted 12 July 2020 - 02:27 PM

I used chalkboard paint; added with laser printer toner, with excellent result.
I hope this helps someone.
Regards.
Edgardo

Chalk board paint is tough. Tough despite being flat. Withstands chalk and wet wiping for years.
Good call.

Edited by stargazer193857, 12 July 2020 - 02:31 PM.

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#22 Visit-the-Moon

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Posted 12 July 2020 - 02:30 PM

Edgardo, that is an interesting idea. Is there a specific ratio that you used when mixing & does the finished product still have that annoying property of chalkboard paint of scuffing easily? Black toner formulations vary but the major component is very fine carbon black, milled to 10 microns or less.That is very fine! The powder is designed to be electrostatic & the polymers bond when heated so avoid warm water in cleanup.

 

Take care when handling toner powder in bulk - the dust is listed as a Group 2B carcinogen. .


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#23 stargazer193857

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Posted 12 July 2020 - 02:34 PM

Candle soot is very non reflective. Not that I would want it in my scope. But I wonder if the toner, being carbon, is just as good. There is the index of refraction of the binder though.
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#24 don clement

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Posted 12 July 2020 - 11:15 PM

Back in the day Nextel was the Krylon 1602 of it's time.

 

Don

 

NextelIMG_5842Web.jpg

 

NextelIMG_5843Web.jpg

 

NextelIMG_5844web.jpg


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#25 Visit-the-Moon

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Posted 12 July 2020 - 11:47 PM

Don, Looks awesome!

 

Mankiewicz Gebr. & Co. sell Nextel branded products, here is an extract from a 2018 tech datasheet for NEXTEL Velvet-Coating. Most distributors are in Europe. Hopefully less of a toxic cocktail now...

 

The Mankiewicz.com website is active.

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