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I need to fix some scratched and chipped paint on a window sill.

I cut off a chip and took it to the hardware store to get a matching sample pot. They scanned the chip and came up with a formula. I gave it a go and, naturally, it didn't match, not even close enough to get away with.

I want to get a match, and now, I have a photo with the colour I want to match right next to the first match attempt.

Since we know the formula for the first attempt, I am wondering if colours/paint work in such a way that we can scan the photo of the first attempt and compare the colour in the photo with the formula from the sample pot, get some kind of delta I'm sure. Then can we scan the colour we want to match and apply the same delta to get the paint formula of the colour I want?

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    Would probably be easier to sand down the whole sill and repaint, than try to match a small section. It is hard trying to match years of fading and dirt. Would need very good(expensive) software to match exactly and different type of light can throw it off.
    – crip659
    Nov 6, 2021 at 13:12
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    +1 to “paint the whole thing”. Depending on its condition, you might get away with lightly scuffing the existing finish, filling scratches, priming, and repainting. If the existing paint might be over 40 years old, test for lead and act accordingly. Nov 6, 2021 at 13:37
  • I've never known a modern scanner fail to get a match on a decent quantity of paint, unless you're not matching paint type like for like. Not sure a sample pot has sufficient accuracy, though, tolerances are too fine. Take it back & complain. There is no way on this green earth you will match from a photo, for reasons you could spend 4 years at university studying in detail.
    – Tetsujin
    Nov 6, 2021 at 15:58
  • Unless your printer is precisely color calibrated you'll never get the right color printed in the first place. Additionally, the paint computers are not designed to calculate a delta between A) and B). They scan the color chip and reproduce it to the best of their ability.
    – FreeMan
    Nov 6, 2021 at 17:35
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    It's also worth noting that small paint samples don't accurately represent the actual color. The machine that puts color into paint has a minimum dispensable amount of colorant. A gallon of paint may require 27 "drops" of one color, 19 of another color, 3 drops of a third, and 2 drops of another. A small 8 ounce paint sample needs 1/16 of each measurement. Since it can't dispense less than a "drop", you probably get 2 drops of the first, 1 of the second, and none of the others. Those small samples are good to decide between red and blue, but not for subtle differences.
    – Mark
    Nov 6, 2021 at 21:45

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I've done semi-professional matching using a Munsell Book of Color, which is a spectral map of the entire color space, using about 1600 paint chips. Note that Munsell is owned by XRite, who also owns Pantone (which is NOT a color space map, and arranges their colors arbitrarily). XRite also makes the paint scanners used at the hardware stores.

It's not easy to do. I have tried to "bracket" the original color using Munsell candidate "chips", capture all in the same photograph with even lighting and all glare carefully eliminated, pull it into Photoshop and compare the RGB values.

It's a huge mess. Most photos are rejected because the original color is not a consistent RGB value left to right and top to bottom, because of a lighting or glare issue. Even when everything seems right, the RGB values don't result in good interpolation because of difference in surface reflectivity, or simply that "seeing colors of light as RGB" is itself a very flawed model.

The only system I've ever found that works is to order full 8.5x11 sheets of the candidate colors, "bracketing" high and low in hue, lightness and saturation, and putting the sheets against the work and eyeballing it.

This would be the equivalent of ordering many sample cans, but the simple fact is, sample cans aren't that accurate for reasons Mark discusses above:

The machine that puts color into paint has a minimum dispensable amount of colorant. A gallon of paint may require 27 "drops" of one color, 19 of another color, 3 drops of a third, and 2 drops of another. A small 8 ounce paint sample needs 1/16 of each measurement. Since it can't dispense less than a "drop", you probably get 2 drops of the first, 1 of the second, and none of the others.

The most effective thing I've ever done is ordered sample cans which "bracket" the target color, and "mixed my own sample" by starting with a few CC's from each can, and then adding a bit more of the color I'm trying to move it toward. It is slow trial and error. Once found, paint some drift cards (properly), compare the drift cards to the original, and if they check out, have gallons made of that.

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