Computers should make painting easy?


So, computers should make painting easy, right?  That’s what I thought when I went to create a custom color for my truck.  But, the truth I found has a different description than “easy”.

I like the 1958 Buick Chieftain’s tropicana turquoise, but wanted a little lighter color for painting my antique 1984 S10 Chevy pickup truck.  It occurred to me that I could find the perfect color on my computer, and then transfer it to a tint mix formula for an automotive paint.  Doesn’t that seem like a reasonable thing to be able to do?

Well, define “reasonable”.  It turns out that paint manufacturers do not use RGB or CMYK for their paint tinting processes.  Benjamin Moore uses something akin to CMYK, but not close enough to do a direct mix from calculated CMYK colors.  Most of the other manufacturers have mix schemes that are nowhere related.  In any case, Ben Moore doesn’t do auto paint.

For starters, LED screens use additive color mixing schemes, as opposed to physical paint, which is reflective, and uses subtractive color mixing schemes.   RGB is additive, and CMYK is subtractive.  So, as a first step we would convert the RGB value from our program (I used Gimp) – to a CMYK value.

So, vision in the physical world (i.e. no LED screens) – is reflective and so is subtractive (light that is not absorbed by an object is reflected, and is what we see).  Emphasis is on the not term  here (which is why LED screens are different).  It turns out that converting from RGB to CMYK is troublesome.  There are a few programs available to do it (Gimp does it, and maybe Photoshop too?)  There are lookup tables (of varying degrees of accuracy), and I’d consult one of those to get CMYK values from the RGB values.

Even CMYK does not work very well in the physical paint world.  That’s because CMYK is a mixing scheme for offset press printing processes.  It’s called “process colors” for that reason.  They print one ink at a time, overlaid.  That’s not what paint does at all!

So, how could I possibly use CMYK in paint?  One way is to use transparent paint.  Transparent paint has a clear binder, so colors can be mixed and overlaid in the fashion of an offset press.   But what a chore to do this on my truck! Also, in printing presses, the colors are not directly overlaid, but instead closely spaced DOTS are positioned to effect the resultant color. Probably, the transparent paints could be mixed and still allow for the analogous process overlay effect – in spite of it’s not being dots.

OK, So we have an RGB value such as [66,176,201], and it can be correlated to a CMYK value like [71,11,0,22].   66-176-201 is the turquoise in the background of figure 1.

But, CMYK throws one more angle at us.  You don’t add white tint to a CMYK color scheme.  That’s because, in offset printing, it’s provided by the paper.  It’s also part of the subtractive quality of CMYK.   That is why the percentages of a CMYK formula do not add up to 100 percent.

So, in our formula, we’ll use a dropper to drop 71 drops of cyan, 11 drops of magenta, and zero drops of yellow.  We’ll skip the black (K), and stir up the first two colors.  Then we’ll add black, drop by drop, until we get the tone we desire.  This is not my idea of computers making painting easier!

I’ll be using E’tac transparent paints, like so:

C   =  Phthalocyanine      (Cyan)

M  =  Quinacridone Magenta     (Magenta)

Y =  Acylide Yellow     (Yellow)

K  =  Shading Black

These are the E’tac company color names.  They are probably not an exact cyan, magenta, yellow, black quintet (but I don’t know for certain).   Obviously we can change the mix ever so slightly, until we get the color we want.  It will take time and patience.  But, once we’re done, what do we do with our CMYK forumla?  No automotive paint manufacturer can directly use it!  Oh, all is lost!  Not really.  We’ll simply paint up a sample board, and let the manufacturer use his paint matching computer to build the custom color for us.  Of course, that means this entire exercise was (somewhat) a waste of time, because we could have printed a page from a color printer to do the same thing.

But, I guess we learned something.

To be continued …

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