Mixing sand with paint to make it darker

[ecormier]

Hi Everyone. I'm working on a mirror box for a 20" dob. I've painted the interior with Rosco Super Saturated Velour Black paint (vinyl acrylic), which is popular with A/V enthusiasts for painting home theaters. However, I must say that I'm disappointed in the paint's apparent lack of blackness. I've recently stumbled upon this article by Gerd Neumann Jr, which recommends mixing sand with chalkboard paint. As I understand it, the sand provides a rough texture to the finish which helps to avoid reflecting light.

I've paid a lot for my Rosco Velour Black paint, and would like to try mixing sand with it before I abandon it for a different kind of paint. Has anyone here tried mixing Rosco paint with sand? Any tips?

The Gerd Neumann Jr article suggests a 1:1 volumetric ratio for mixing as a starting point. I'd like to hear what mixing ratios worked well for you.

I found a home improvement article that recommends mixing play sand to create a non-slip painted floor surface, so that's the stuff I plan to use in attempting this.

I will test on a piece of scrap wood of course, but hearing what worked well for others would be great.

[Mr H in Yorkshire]

I have used this technique in a home build scope. Looking obliquely along the painted surface, it is actually quite good. I used sawdust - any particles escaping are less dangerous to glass. I applied the paint then threw in the sawdust and rolled it around. Once dried applied more paint.

[Peter Drew]

I've used a similar technique using sand, sawdust or fine aluminium filings.  Breaking up a black surface is really effective, specially on the inside of baffle tubes in small Maksutovs/SCT's which tend to be very reflective.      🙂

[John]

Some Tele Vue refractors use a form of sandpaper painted matt black to line the inside the scope tubes. It seems to work pretty well.

 

[ecormier]

18 hours ago, Mr H in Yorkshire said:

I have used this technique in a home build scope. Looking obliquely along the painted surface, it is actually quite good. I used sawdust - any particles escaping are less dangerous to glass. I applied the paint then threw in the sawdust and rolled it around. Once dried applied more paint.

I have to do all my wood cutting outside, so I unfortunately don't have a means to collect the sawdust in a clean manner.

Edited September 28, 2023 by ecormier

[ecormier]

14 hours ago, Peter Drew said:

I've used a similar technique using sand, sawdust or fine aluminium filings.  Breaking up a black surface is really effective, specially on the inside of baffle tubes in small Maksutovs/SCT's which tend to be very reflective.      🙂

Do you remember the mix ratio you used with sand?

[Mr H in Yorkshire]

 

 

I will butt in here with my method. I didn't proportion the mix, I simply painted the interior surfaces, then while wet put the sawdust in and simply shook/rolled it around to let it adhere. I did this twice. The surfaces of my scope comprise both wood and aluminium and it works equally well on both.

My feeling is that if you mix the sawdust then paint with the mixture you will get a preferred orientation to the particles, which may be a good thing. If I look into the interior of  the telescope housing, the random orientation bestows an equal darkness in all positions. The particle/paint surface is definitely darker than black paint alone but I can't put figures to it. Also I used blackboard paint which is inherently matte finish. I did consider a scheme using PVA glue first, then sawdust then paint. I'm sure that would work too.

[AndrewRrrrrr]

can recommend this:  https://culturehustle.com/products/black-4-0

as long you are not associated with Anish Kapoor!

 

[MartianHill]

Not sure sand in an OTA is a good idea in the long term but sawdust is 👍

[skybadger]

Wilko sticky backed velour ?

[Chaz2b]

I’ve used Stuart Semple blackest black to great effect! Had to be carefull though as if you show it to any light it turns into a black hole! Lol

Bought mine on ebay, it’s an acrylic paint and doesn’t need sand I can assure you. Would be easier to apply.

chaz

[fwm891]

Blackboard paint mixed with sawdust… it doesn’t have to be dead black just kill reflections

[ecormier]

I checked out the play sand at the local building supply store, and was not impressed by its cleanliness. I see many here recommending sawdust. The next time I do some wood cutting outside, I'm going to try laying down a tarp to catch the sawdust. I might also try asking a local cabinet maker.

As for the Stuart Semple Black 3.0, it's a whopping $300 a litre, and I've read several negative reviews about it being greyish and not durable. I'm hesitant to spend that kind of money on it.

[Mr H in Yorkshire]

@ecormier There is something ironic about having  a problem getting sawdust and living in Canada. It's not exactly strapped for forests. Mind you lumber yards saw dust would probably be way too coarse.  😊

[Zermelo]

Sand from a builders' merchant is often not too clean. Sand for horticultural purposes is usually washed (to remove salt).

Sawdust may be a better option - preferably from a cabinet maker, as suggested, since the cut is finer.  Or, what about trying some of the finer grade sawdust sold as scatter material, used by railway modellers and wargamers? Something like this:

https://www.ebay.co.uk/itm/166026936498?hash=item26a7fa00b2:g:4F8AAOSwhwVhCCG4

[Chaz2b]

11 hours ago, ecormier said:

I checked out the play sand at the local building supply store, and was not impressed by its cleanliness. I see many here recommending sawdust. The next time I do some wood cutting outside, I'm going to try laying down a tarp to catch the sawdust. I might also try asking a local cabinet maker.

As for the Stuart Semple Black 3.0, it's a whopping $300 a litre, and I've read several negative reviews about it being greyish and not durable. I'm hesitant to spend that kind of money on it.

As to price, it’s £49.95 a litre on ebay. I bought just 10ml, other sizes available. As to colour, mines black! No sign of greying, but it does require a good stir before use. Don’t know about durability as I only applied it last month.

chaz

Edited November 1, 2023 by Chaz2b

[apaulo]

if you want fine sawdust empty it out of any wood sander bag

[fwm891]

5 hours ago, apaulo said:

if you want fine sawdust empty it out of any wood sander bag

That’s sanding dust and probably too fine unless a really coarse graded abrasive is used.

[saac]

Had my first year science class doing a decomposition reaction  with Copper Carbonate (lovely green coloured powder) this morning (yes we do experiments in school still) and the results made me think of this thread.  The resulting copper oxide even had the kids commenting on just how jet black it appeared. I'm guessing it wouldn't be a simple matter as mixing copper oxide with some glue (pva etc) so that it could be used as a very non reflective black paint but it did cross my mind. Looking at uses of copper oxide I found that it is used amongst other things as pigment in anti-fouling paint (marine application).  The resulting powder is very fine and it's flat non reflective nature is really cool. 

Jim 

 

[Mandy D]

9 hours ago, saac said:

 

That gas tap is real old school and identical to the ones we had in my school back in the 1970s and they were old then. I'm pretty sure Michael Faraday used ours ... 😁 The bench tops look simiar, too.

[saac]

11 minutes ago, Mandy D said:

That gas tap is real old school and identical to the ones we had in my school back in the 1970s and they were old then. I'm pretty sure Michael Faraday used ours ... 😁 The bench tops look simiar, too.

Our school was built in the 1950s and the science labs, save two which have been refurbished, have all the original fittings and fixtures. The desks are solid teak and carry the scars and musings of the pupils down through the years - "Bobby was here" ! 

Jim