"bronzing" ?

Discussion in 'Digital Darkroom' started by screeny, Apr 28, 2006.

  1. Ok sorry to ask but my English isn't that perfect: What is meant by
    "bronzing"? I have read it many times in printing related threads but
    can't figure out what is menat by it.

    thx for answering this question *shame*
     
  2. Pigment inkjet printers often mix other colors with the black ink. On glossy, and semi-glossy paper, pigment ink has a gloss differential problem (lightly inked areas look glossy, heavily inked areas look matte) - and the slight tint to the black ink causes a color shift that makes the black ink look bronze in color when viewed at an oblique angle.

    The Epson K3 inks and new Canon pigment inks have cured the bronzing problem, but there is still a slight amount of gloss differential between heavily inked areas and lightly inked areas on semi-gloss and glossy paper - UNLESS you use the Photo Black ink cartridge and not the Matte Black. Use of Photo Black all but eliminates gloss differential. The tradeoff is that the Dmax (maximum shadow density) that can be produced is also reduced using Photo Black.

    Dye ink printers don't have either gloss differential or bronzing problems - but there are a whole host of other considerations to be taken into account when using dye ink printers. The chief one being print longevity, which can match pigment inks IF the ink and paper are matched correctly.
     
  3. I disagree with the foregoing statement. Bronzing is an effect almost exclusive to dye-based printers. Soluble dye is normally absorbed in the surface. Where it is unable to penetrate fully, as in especially dense areas, it dries on the surface with a metallic bronze-like color. It is a phenomena familiar to anyone who has worked with soluble dyes as used in wood staining.

    Pigment-based inks are not absorbed much at all in the paper surface, and cause the reflectivity of the surface to vary depending on the density and coverage. Epson (and perhaps others) partly overcome this problem by having two types of black ink depending on the application - "Photo" black for semi-gloss paper and "Matte" black for matte papers. Pigment ink may exhibit metamerism, in which the color appears different in different types of light, and was a problem with the Epson 2000 printer. Metamerism has largely been eliminated in the 2200 and subsequent printers.
     
  4. MI,
    I think Steve is more on target and has explained the reasons OK. It's our expierence at the lab that bronzing is an issue with hybird pigmented ink sets on any glossy stock ink jet paper. Example: Ultra-Chrome which I think most people would classify as a pigment rather then dye ink set, exhibits plenty of bronzing. For us it was more of an issue with grayscale printing then with RGB. The bronzing with RGB was always kinda hidden because of the colors, but Grayscale we lost a bunch of biz because 1/2 of our customers couldn't get past the bronzing and gloss diferential problem. I'm glad to report that on the new K3 Ultra-Chrome 98% of these problems have been cured. We haven't had any of our customers who rejected the old ink set reject the new. As far as dye goes, because it penetrates the surface fully, we find that there is no bronzing problem but matamerism (where a print can look different in different lighting. Daylight to tungsten) was a big issue. By the way we found a lot of matamerism with the old Ultra-Chrome ink set, specialy when you did RGB sepia tones. And keep in mind that bronzing is not an issue with mat or "Art Papers" because the ink penetrates more fully and is not sitting on a glossy surface. The other interesting thing to note is that we have found that the more the glossy surface's bite the more bronzing and gloss differential you have. Meaning more on a Luster or pearl, less on a glossy or smoother surface like semi-mat.
     
  5. "I disagree with the foregoing statement. Bronzing is an effect almost exclusive to dye-based printers."

    Then you've never seen the output from the Epson xx600 series printers & Ultrachrome inks. B&W and color prints on glossy and semi-gloss paper show bronzing. Or, maybe I was just imagining the whole thing when I was using my 9600? This is documented in Harald Johnson's book, "Mastering Digital Printing." Maybe Harald was imagining it too...

    As Ira has stated, the K3 inks have solved bronzing, but I still can see some slight gloss differential with matte ink on glossy or semi-gloss papers. I use an Epson 9800 for reference.

    The best semi-gloss paper to date with K3 Matte that I've found is the Breathing Color Vibrance Semi-Gloss. I have yet to get my hands on enough samples of Crane's Silver Rag paper to properly profile the paper and setup an environment in the RIP.

    If you overspray a print the gloss differential goes away as the inks are evenly wetted by the spray. However, the problem with glossy papers is getting an even coat that does not disrupt the smooth surface, and make small wavey areas that can be seen when viewed at oblique angles.

    That never sounds like a problem until you hang the print on the wall and walk by it. Then you're well aware of the print's uneven gloss surface as it slightly, shimmers and moves as the light reflects off of the very slight dips in the coating.

    To solve this problem, some people use a laminate film over the print, while others have confected dip tanks that roll the print through the liquid and evenly squeegee it off making a smooth coating. The film laminate is really the best way to go IF you have the space to setup the equipment.

    Me - I just print on semi-gloss and matte papers and over spray with a satin or custom mixed (gloss + matte) overcoat using a SATA Mini4 HVLP spray gun.
     
  6. I have never seen "bronzing" from my Epson 2200 in the sense I defined above - clearly metallic in appearance. On the other hand, it was common in my dye-based 1270. I do see variations in reflectivity on Premium Luster paper depending on ink coverage, and to a lesser extent on matte paper. The reflectivity of matte paper prints is also affected by handling and abrasion. Neither effect is attractive, but I think we disagree on nomenclature.
     
  7. "...but I think we disagree on nomenclature."

    Okay. Then what do YOU call it when a black area turns metallic looking and slighty red or yellow depending how much of what color ink was mixed into the black?

    Bronzing is the closest description - but, I'm certainly open to a different term. You'll still have to convince Harald Johnson that it's NOT bronzing, however.

    BTW - the results from your 2200 are NOT transportable to the results from Ultrachrome with an xx600 series printer. While they both use "Ultrachrome Ink" the formulations are not the same for small format and large format printers. The Ultrachrome designation only describes a resin encapsulated, pigment ink system - not the ink formulation itself. Otherwise, a profile for a 2200 would work on a 9600 - or vice versa - it doesn't. Also, the machines lay down the ink differently in dithering patterns, droplet size, etc.
     
  8. Well, it looks like M.I.'s question has been addressed, so that just leaves the slightly heated debate between Ed, Steve, and Ira. I hope this cools things down, rather than makes it worse.

    First, there's only one original UC ink formulation, common to the 2200, 4000, 7600, and 9600. You can drain the 110ml or 220ml carts from the large format printers into bottles and load them into 2200 carts, and the 2200 colors will be perfectly normal, no need to fiddle with driver settings or make new profiles. The 2200, 7600/9600, and 4000 do differ substantially in dot size and dither pattern, with the 7600/9600 being the largest drops and the least sophisticated dither, the 2200 next, and the 4000 having the smallest drops and the best dither.

    Original UC exhibits both bronzing and gloss differential. All the pigments are acrylic encapsulated. The gloss of the encapsulant varies from color to color of ink, and it is nowhere near close to the gloss of the resin coated (gloss, semigloss, or luster) papers.

    The encapsulant on both full strength and "light" black is also prone to real, honest-to-God bronzing. It's even "bronze colored" at some particular shades of gray. This effect is reduced substantially by the "black generation" strategy of Epson printer driver. Black generation refers to how you make neutral colors: how much of the neutral color is made by using the nearly neutral black and light black inks, and how much is done with a mix of cyan, magenta, and yellow in the proper proportions to make a neutral tone. The Epson drivers use a lot of CMY in neutral grays, more CMY than K, in fact. Since the colored pigments have less bronzing than the black, this hides a lot of the bronzing, but causes other problems that we typically find to be even worse.

    The Epson cyan, magenta, and yellow (especially the yellow) exhibit a high degree of illuminant metamerism: they appear to be different hues when viewed under different light sources. This is, for lack of a better term, really bad.

    When using a RIP that allows you control black generation, it's customary to print B&W images using only black and light black, with just enough CMY to adjust tone. Black typically outweighs color by at least 2:1, even for strong cool or sepia tones (there's virtually no color added to warm tones, the Epson black is rather warm all by itself).

    The new Epson K3 inks are a considerable improvement. All colors are free of bronzing. Epson has done a better job insuring that all the colors match each other (and RC paper) in terms of gloss. They use three dilutions of black, and the black generation in the drivers is set up so that as much black is used as possible to form neutral grays and any even remotely neutral colors (this is also great for ink utilization). The 4800, 7800, and 9800 all use the same drop size and dither (indeed, they use the same print head, first debuting in the 4000). I think the 2400 has an edge on them in terms of dot size and dither. Since the K3 machines lean so heavily on the black both for finesse in controlling light tones and for muscle in building density in dark tones, Epson was free to create new cyan, magenta, and yellow that trade off for saturation. They can "tone" the 3 shades of black for very nice colors near the neutral axis, and hammer home saturated colors far from neutral.

    And that is the whole story.
     
  9. jtk

    jtk

    Without pretending technical expertise, I'll just say that my Epson 2200 with Epson OEM pigments produces differing amounts of bronzing with different glossy papers...the very least with Kirkland (Costco) and Moab Kokopelli. This is of course entirely unrelated to gloss differential, but Kirkland/Kayenta are also the best in that respect.

    Bronzing is never present in matte prints (such as EEM or my favorites, Moab Kayenta or Entrada) except when I print B&W and overload black with the slider in QTR (never happens at default settings unless I'm printing at 2880). The new faux "air dried glossy" papers seem not to bronze with 2200/OEM (in print exchange samples) but they have other issues.

    With QTR it's possible to reduce bronzing to near-nil with some images on the two good glossy papers through subtle use of the ink control slider. The challenge is to avoid desaturating the blacks when reducing black ink below default/neutral level...it tends to be trial and error.

    The ink control slider in QTR is rarely mentioned, but it's an elegant and intuitive tool that directly controls the amount of ink being deposited while minimally changing the overall image. It can add density relatively selectively (increasing DMax without darkening the print overall or changing overall contrast) and it can reduce (or create) bronzing.
     
  10. "Bronzing is an effect almost exclusive to dye-based printers. Soluble dye is normally absorbed in the surface. Where it is unable to penetrate fully, as in especially dense areas, it dries on the surface with a metallic bronze-like color. It is a phenomena familiar to anyone who has worked with soluble dyes as used in wood staining."

    Dyes are popular becuse they are widely known for not causing bronzing, and because of more brilliance (chroma) from higher Dmax. However I have seen bronzing happen using dye. I decided to try HP Premium Glossy paper with Epson inks, and boy did I get a lot of bronzing. It is like the dyes were not strong enough to absorb in, yet with HP130 printers(vivera inks) no problem with same paper. Match mfr brand of printer with same brand of paper and dyes should not give a problem. UC ink is well known on the other hand for bronzing using glossy. Just look at any article for UC ink and glossy.
     

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