willie_901
Veteran
Ask the poor paint store peron how to turn blue paint white.
I want 18% middle gray what do I tell the paint guy at home depot?
- Thread starter 68degrees
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68degrees
Well-known
what can I say? Im a tight azzz
Richard G
Veteran
I'm just watching still, seeing if the OP can get Roger to buy that blue paint off him to paint his Land Rover with.
Roger Hicks
Veteran
Nah, unnatural. Green is the proper colour, but cream and maroon are OK. It was a present, after all: Frances bought it for me. She thinks ALL cars should be red (both hers are) but maroon is close enough...
Cheers,
R.
Peter_wrote:
Well-known
willwright
Member
you might contact the Harry Ransom center at the UofT in Austin...they have an 18% grey viewing room, with color correct indirect lighting. Perfect viewing.
Roger Hicks
Veteran
Facinating: I didn't know about this. Thanks. But 'perfect' in what sense? While I agree that it is 'perfect' in one sense, it would be hard to create an environment less the (extremely diverse) settings in which photographs are normally viewed, so it could also be taken as totally useless. This needs some thinking about...
Cheers,
R.
sepiareverb
genius and moron
That's not mixed from black paint and white paint tho, that's grey paint mixed from colored paints. You wanted to know how much black and white to mix didn;t you?
I can say with almost complete certainty that it is some of each. A little bit of black and a good bit of white.
Really the most entertaining thread in years.
68degrees
Well-known
yes I still havent found that out but its a start. Ive learned so far that 18% reflected light off a surface depends on the texture of the wall as well as the mixture of dark and light paint and the finish ie matt, flat, glossy, semigloss, eggshell, and the brand, and the batch etc etc, and that it can be any color. The color only important for human beings viewing photos but unimportant for calibrating light meters (which I now understand are for wimps and pussies) and camera shutters.
However nobody can tell me how much difference there would be between a smooth wall with a given color and sheen paint, and a textured wall (such as on drywall) with same paint. How much different could it be? Are we talking about tenths of a percent difference in reflectivity or less than 5% difference etc etc. Nobody seems to be able to quantify it or even estimate.
How much difference in reflectivity can there be between brands, or batches of paint. Is it hundredths of a percent all other things being equal?
Also if i were to make a gray card (which are for pussies and wimps), not that I ever would but IF i did, what instrument would I need to measure what percent reflectivity it is? No one has answered that either. I suuppose I could by trial and error arrive at the formula for the right mix of black and white paint to come up with 18% reflectivity on a given surface, with a given sheen, and a given brand.
Yes Im learning a lot not just about 18% gray, but also on how anal some people can actually be. What level of precision is required here? How scientific must this be? To my knowledge no lives or limbs are hanging in the balance to get this dead on balls 18.000000000000001% reflectivity.
I still want to know what ratio of white and black paint will make a 18% reflective surface on a smooth flat surface.
When contemplating the words smooth, flat, black, white. and so forth, simply pick a precision you are comfortable with and estimate and include variances so I can get an idea of how much difference it might make.
Remember this is no longer about gray cards or calibrating or viewing photos in a perfectly neutral viewing environment. This is only for the sake of knowing how much black and how much white makes 18% reflectivity with a range depending on variables such as brand, batch, texture etc.
sepiareverb
genius and moron
Perhaps it is 18% black paint.
Gabriel M.A.
My Red Dot Glows For You
Do you believe middle grey would work in the dark? Or black, perhaps? Why not darkroom red lightbulb red? Or maybe stop bath indicator purple? Hey, it's all photographic.
For "middle grey", you could bring a middle grey card to a competent paint mixer so they could match it. You could google your local Lowe's or Home Depot. Paint matching is usually what nonindustrial furnishers do.
68degrees said:
Yeah, then there's that, the FG Factor.
68degrees
Well-known
I was thinking 18% white paint. Thats what makes sense to me but I have no way to measure the reflectivity of a finished wall. I thought white reflects 100% and black reflects 0% so 18% reflective would be 18% white but then someone said only a mirror reflects 100% light not white. I think the only way to actually know and find out how much variance there would be depending on brand paint, batch, wall texture, sheen etc is by actually trial and error and measuring it with some kind of device that I am not yet familiar with.
68degrees
Well-known
Would it work? Ya I think it would reflect 18% of 0 if it was totally dark.😀
If there was a safelight on it would be a lot darker than if the wall were white although we dont know how reflective white walls are either, would be nice to know then I could calculate the ratio of white and black.
sevo
Fokutorendaburando
Only if both paints contain equal amounts of pigments of identical particle size, absorption characteristics and distance from the ideal 0% respectively 100%. Which they will not, in real life. White wall paint in particular tends to be a emulsion (or later, in dried state, dispersion) of essentially transparent particles (whose apparent whiteness is the result of a immense number of partially reflective particle boundaries) in a equally transparent vehicle, so that even minor amounts of a colouring additive will colourize and darken it far more considerably than you'd expect by volume. In my experience, mixing a middle grey from common wall paint will often take much less than 10% black (rather than the above 82%).
Roger Hicks
Veteran
And I'm afraid it's still a meaningless question because there is no such thing as 100% reflective white or 0% reflective black. Nor does 'smooth' mean very much.
Consider black velvet and black paint, both 'smooth'. Shine lights on them from different angles. On of the reasons velvet is so black is that light gets 'lost in the holes', reflected back to and fro between the fibres, a little more being absorbed each time. This is also why matte black paints (such as blackboard paints) are blacker than gloss black paints.
Now consider white paint. It is very hard to get a white paint that is as white and reflective as fresh snow, or a magnesium carbonate block. White blotting paper and fresh white paint reflect about 1/3 stop less than those 'standard' whites. Even slightly weathered white paint can lose another 1/3 stop.
Finally, consider the medium you are going to use to suspend the pigments. Are you going to make it thin, so the pigments come out matte, or thick, so the paint is shiny?
As I've said before, there are just too many variables. You are looking for a precision that does not and cannot exist. Sure, you can take any two paints, one black and one white, and mix them together to get an 18% grey, compared directly with a standard 18% card bought (on faith) from any reputable manufacturer. This would ONLY hold good for the two paints you mixed, though, because there are no absolute black paints or absolute white paints.
Now paint your mixture onto a variety of 'flat' surfaces: board, concrete, rusty sheet steel, glass, whatever you can find. They'd probably all look quite close to the paint as measured, as long as they were wet, but even the, I doubt they'd be identical. As soon as they dried down, they'd almost certainly be darker.
The only answer (as you have already surmised) is to get some white paint, and quite a lot less black paint, and mix them until you've got paint that's a little lighter than a reference grey card (to allow for it darkening on dry-down); paint it onto a variety of surfaces; wait for it to dry...
Cheers,
R,
wolves3012
Veteran
Ok, I spent 25 years working with colour and paints of various sorts - from domestic to automotive and others. Let me try and point out some of the more important reasons why it can be so complicated....
First, white paint isn't 100% reflectance, nor is it a pure white with no colour at all. Ask a car-paint dealer how many "white" paints there are - hundreds!
Second, white paints are not all the same. For various cost and quality reasons, all manner of fillers are added and different resin types used. Together with varying qualities of "white" pigment (Titanium Dioxide).
Third, black pigment is varying types and sources of carbon-black (furnace blacks, lamp black and channel blacks and a few others). Carbon-black pigment isn't a pure black, when you "dilute" it with white it can become a yellowy-grey, a bluey-grey and so on. So now, you no longer get pure grey and have to add other colours to the mix to stay neutral gey, on that perfect line between true white and true black.
Fourth, add in much the same factors as under "second", for your black.
So, there is a combination of a manufacturers paint that will give 18% neutral grey, sure. Change any one factor from dozens and that formula is now quite noticeably off.
So, yes, it really is that complicated. And I didn't even begin to mention the differences between gloss/semi-gloss/eggshell/matt and so on! Nor the surface you paint it on.
The instrument you need to measure the colour and reflectance is called a spectrophotometer. When you look up the price, you'll decide you can live without an exact 18% grey!
Suggestion: go to a paint store that does a colour-match service. Get them to scan an 18% grey card and produce a match in matt (flat). Paint it on your walls and accept that it's plenty near enough in the real world. Job done, get some sleep.
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wolves3012
Veteran
Actually Roger, that's not how it's done at all but your point is still quite valid...
Roger Hicks
Veteran
Fair enough. I was just thinking of variations in reflectivity when you dilute paints, and the different effects of different oils when you are grinding paints for oil painting on canvas. I hope there was at least a grain of logic in that!
Do you know the story of the man who was painting one of those New England white wooden spires? He didn't have quite enough paint, so he kept diluting it a little more... then a little more... then a little more.
When he'd finished, he stepped back to look it it. It was... OK. Probably the congregation would think it wasn't too bad. But then, a great voice spake unto him from heaven: REPAINT! AND THIN NO MORE!
Oh: and thanks for the other information, too. Your point about 'get a paint company to match an 18% grey card, and call it close enough' is of course the best advice in the whole thread.
Cheers,
R.
sepiareverb
genius and moron
Still the best thread in ages. Keep it coming.
wolves3012
Veteran
Artists paints Roger...apples...oranges ;-)
Not heard the joke, that made me chuckle!
Actually, for most commercial paints, specifically domestic paints, the simplest way is to add a matting agent (usually silicas) to a gloss formula. Often there's also china clay added because it also reduces gloss, whilst adding to opacity and lowering cost (cheaper than TiO2). That's something of an oversimplification because there are other and cheaper ways, depending on intended applications. Things like automotive paints tend not to be in demand in other than gloss, few people want a matt car! Although, I've seen it done...