Why is my black painted tank back light grey?!? - The Planted Tank Forum
 
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post #1 of 12 (permalink) Old 12-08-2014, 12:59 AM Thread Starter
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Why is my black painted tank back light grey?!?

I have a 220 and want one side covered where the plumbing is; it is about 24" by 30". I bought some typical black aquarium paper thinking it was a full 24" but it's not.

Rather than piece it I decided to paint it. Bought a sample size from Lowes of a latex called "very black".

Started painting and it was very grey. Light grey. Got a tiny bit darker as it dried. I stopped after a small section as this is not the color I want.

It's easy to take this off but... when I painted a piece of wood with this color it is, well -- very black.

What am I missing here? I've got another tank with black paper (applied with olive oil) and it is quite black, much moreso than this, with the same light fixture.

Is there a particular type of paint - gloss, flat, semi-gloss - that is better?

I cleaned the glass thoroughly first, but I did not treat it in any way.

Any ideas?

Here's the plywood next to the painted side (through the water of course).


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post #2 of 12 (permalink) Old 12-08-2014, 01:46 AM
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I would guess that the more gloss in the paint to more it would diverge from the intended color. I have no experience with this but it's what the art school kid inside of me is thinking.


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post #3 of 12 (permalink) Old 12-08-2014, 10:21 PM
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huh. That's rather strange.

I've painted a couple tank backs with a sample-size latex I got from either Home Depot or Lowe's (can't remember which...)

Mine looks pretty much the same inside and out, except the outside has a bit of visible texture from the brush marks.

Is there any light sources that could be coming through the paint on the tank, making it look grey?

When I paint my tank backs, I keep adding coats until I can't get a flashlight beam through from the inside of the tank.

Anyways, I'm curious to see if anybody knows what might cause this...
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post #4 of 12 (permalink) Old 12-08-2014, 10:56 PM Thread Starter
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Originally Posted by lochaber View Post
Is there any light sources that could be coming through the paint on the tank, making it look grey?

When I paint my tank backs, I keep adding coats until I can't get a flashlight beam through from the inside of the tank.

Anyways, I'm curious to see if anybody knows what might cause this...
No, dark behind it.

The only thing I can see that is causing it are very bright lights right above it. In the past when I've seen this the lights were running lengthwise down the tank (as are mine) and the painted side was the back, parallel to the lights. Mine is the end, so there are a pair of fixtures shining light directly down onto the side.

With a bit of trepidation I took some really black, glossy oil paint (rustoleum) and painted a small portion this morning. After drying it was very slightly darker, but it also looked grey.

I can only assume it's something about the light, the glass, the angle, etc.

So I rolled the whole side this evening, waiting for the first coat to dry (it's pretty thin, I can see a lot of light looking in toward the tank). But it looks fairly evenly grey from the other side.

But it really bugs me how grey it looks. However it's not that noticeable if one just walks up to it, and it hides the plumbing and frame.

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post #5 of 12 (permalink) Old 12-09-2014, 12:46 AM
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Got something weird going on but I have no guess what. Since you have no fish yet, how about sticking the wood, which looks black enough, in the tank and moving it around to see how it looks when looking at different ways for the light to hit? I paint most tanks backs and bottoms with most any type of black paint and never got grey so far. I paint the bottoms so that when it gets exposed the fish don't act so goofy trying to swim down through the bottom.
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post #6 of 12 (permalink) Old 12-09-2014, 12:48 AM Thread Starter
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Got something weird going on but I have no guess what. Since you have no fish yet, how about sticking the wood, which looks black enough, in the tank and moving it around to see how it looks when looking at different ways for the light to hit? I paint most tanks backs and bottoms with most any type of black paint and never got grey so far. I paint the bottoms so that when it gets exposed the fish don't act so goofy trying to swim down through the bottom.
I've got fish and a fully planted tank. This is the outside I'm painting.

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post #7 of 12 (permalink) Old 12-09-2014, 02:01 AM
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Whoops! Not watching you close enough??
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post #8 of 12 (permalink) Old 12-09-2014, 02:25 AM
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The glass is transparent. The wood is not. You'll need to build up the paint until it's thick enough that light won't pass through it.
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post #9 of 12 (permalink) Old 12-09-2014, 02:29 AM Thread Starter
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The glass is transparent. The wood is not. You'll need to build up the paint until it's thick enough that light won't pass through it.
Yeah, but there's no light behind it.

However, I am doing as you suggest anyway -- second coat just went on. I'm judging by not being able to see the tank light through it from the outside. Two coats looks about right, it should be dry in a couple hours which means in the morning for me.

It's still weird. I have another tank with the same light, which has black paper, and it is much more black. Tomorrow when I get some time will set that light perpendicular and see what it looks like in comparison, maybe measure relative reflectivity.

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post #10 of 12 (permalink) Old 12-09-2014, 02:31 PM
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Coud be a second coat will help but when painting mine, the first coat never looks grey but just has streaks where the light shines through. But then I don't remember ever filling the tank to look at it through water. May be something that we have not noticed just due to the way we have done it?
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post #11 of 12 (permalink) Old 12-09-2014, 05:06 PM
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Water in the tank changes what happens to light striking the back glass. Water makes the light pass through the glass at almost all angles, but be reflected off the back surface of the glass when the back is clean and unpainted. With the back painted, the light should all be absorbed by the paint, so it should look black. This seems weird!!

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post #12 of 12 (permalink) Old 12-10-2014, 12:13 AM
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well, this doesn't help your situation much, but I'm sorta glad I'm not the only person who finds this a bit strange and confusing...



Anyways, the only other thing I could think of is maybe try cleaning a spot on the glass really, really well, with a solvent like acetone or alcohol or something. Maybe there is some weird residue that's causing the gray color, or reacting with the paint or something...

I don't know, that's really strange. I have no idea why it looks black on wood, but grey on the inside of the tank...
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