Assigning Pantone Colors to Heat Treated Metallic Objects
I need some advice on how to approach a project. I received a color management assignment from an engineering company. They heat treat metal and are in the process of preparing some polished steel discs (semi-matte, not a mirror finish), then heat treated. As the heat treating temperature changes, so does the final color of the heat treated sample, apparently quite reliably. They want me to determine the Pantone color that comes closest to each heat treatment temperature. Their final goal is to hand out printed samples that reliably reflect the temperature at which a sample was heat treated. Sounds simple. My first challenge will be getting reliable L*a*b* readings for a decent match. Just to experiment, I tried sampling the matte aluminum surface on the back of my iPhone directly using my i1Pro spectrophotometer, and got a Lab reading of 77L, -1.1a, 1.5b using D50/2° (5 different samples were all very close). Using the color picker in Photoshop (whole Lab numbers only), it says that Pantone Cool Gray 4C (Pantone Solid Coated Library) is the closest match. If I use the Pantone Premium Metallics Library, it gives me 10103C. They want me to print a few dozen accurate color charts on my Epson printer and semigloss paper, so I will have to use the Pantone Solid Coated Library. I'll probably create the file in Lab color space using the equivalent Lab numbers for each Pantone color. Here's my problem… When I hold the printed Cool Gray 4C from my Pantone swatch book against my iPhone, the Pantone sample looks a lot darker than my iPhone. Of course, if I tilt the iPhone so it receives less direct light, it gets darker and approximates my 4C sample. I'm confident the Lab values are correct. The a* and b* color data is probably quite usable, but I suspect getting a suitable brightness level that prints so it looks like the sample is going to be difficult. It's like photographing any shiny metallic object (like silverware)…I can make the object appear pure white, pure black or any shade of gray I want, depending on my lighting and the family of angles. Hmmmm. If reading directly with a spectrophotometer doesn't work well, I guess I can photograph the samples under controlled lighting, but I am faced with the same dilemma, because I can make the metal as bright or as dark as I wish depending on the lighting setup. Does anybody have experience and advice on how to proceed? Thanks, Lou Dina
On Mar 31, 2014, at 1:42 PM, Louis Dina <lou@loudina.com> wrote:
When I hold the printed Cool Gray 4C from my Pantone swatch book against my iPhone, the Pantone sample looks a lot darker than my iPhone.
Why is the incorrect preview on a non color managed phone an issue? Andrew Rodney http://www.digitaldog.net/
On Mar 31, 2014, at 12:42 PM, Louis Dina <lou@loudina.com> wrote:
Does anybody have experience and advice on how to proceed?
If you're going to be printing with true metallic inks, you might be able to get a not-miserable match just by getting the closest Lab match you can. The difference in specular reflections will still be there, but they might be acceptable. If you're going to use regular inks or en electronic device for the final presentation, no single solid patch of color is going to be adequate. Rather, you're going to need to photograph the metal using techniques similar to those that you'd use in photographing coinage. Essentially, you don't photograph the metal, but rather the reflections, especially of the light source(s). Particularly helpful is what's sometimes called, "black magic," portions of the subject that, due to the geometry of the lighting, reflect almost no light back to the camera and appear nearly black. Nearly- or even fully-blown-out specular highlights might be desirable as well. Depending on the shape of the object, there might only be a very little bit that's actually the color reported by the spectrophotometer. You could simulate that type of effect in Photoshop, of course, but it'd be a lot easier for me personally to photograph it than to do it digitally. That'd especially be the case if you needed the highlights and shadows to be accurate as well. Another option to suggest to the client is that they might to want to just make sample books with the actual materials themselves. It'd be the only unambiguous option, and may well lie within the budget -- especially if the requirements are particularly stringent or critical. Cheers, b&
Ben Goren wrote:
Another option to suggest to the client is that they might to want to just make sample books with the actual materials themselves. It'd be the only unambiguous option, and may well lie within the budget -- especially if the requirements are particularly stringent or critical.
This is a really good suggestion. What you could concentrate on then, would be a scientific means of quality assuring the samples. Quite apart from the difficulties of measuring metallic samples in a scientific way (although there are multi-angle instruments that will attempt this), accurately reproducing such a color so that it matches under an arbitrary illuminant involves its spectral and geometric behavior (BRDF). No ordinary printing process will manage this, and the whole project is rather bleeding edge from a normal color reproduction point of view. Graeme Gill.
On Mar 31, 2014, at 2:58 PM, Graeme Gill <graeme2@argyllcms.com> wrote:
No ordinary printing process will manage this, and the whole project is rather bleeding edge from a normal color reproduction point of view.
Just to expand upon Graeme's point: it's not possible with standard inks, and any non-standard printing / inking technology (such as with Pantone metallic inks) will either be a rough match at best or a much bigger project than simply using samples of the actual material. If that's too expensive (etc.) or if a regular print is "good enough," then you likely want a representative photograph as I described. b&
On 31 Mar 2014, at 20:42, Louis Dina <lou@loudina.com> wrote:
Does anybody have experience and advice on how to proceed?
Yes, you need a different measuring device. You can get spectros that are made to measure reflective surfaces — they illuminate and measure over a range of angles. -- Martin Orpen Idea Digital Imaging Ltd
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 Hello Louis and all I would try to find a metalized inkjet substrate with similar gloss to the steel samples , which is slightly brighter than the original saples. Make a profile of this substrate and be prepared, that you need further manual corrections. To manage the customer color expectations: Tell him, that standard Pantone colors are not a practical reference (recommend Pantone Metallics) Also explain, that normal semigloss paper is not an appropriate subtrate for this job. You also should define a lightning enviroment (e.g. GTI or JUST), in which the original smaples and master prints are viewed for a color OK. If the samples are matching after visual fintuning the print out, you can remeasure the finetuned print and define this L*a*b* colors as reference for the print substrate and lightning environment. Regards Jan-Peter Am 31.03.14 21:42, schrieb Louis Dina:
dark as I wish depending on the lighting setup.
Does anybody have experience and advice on how to proceed?
Thanks,
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participants (6)
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Andrew Rodney
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Ben Goren
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Graeme Gill
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Jan-Peter Homann
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Louis Dina
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Martin Orpen