Re: GRACol Paper classification
Re: GRACol Paper classification
- Subject: Re: GRACol Paper classification
- From: Matt Louis <email@hidden>
- Date: Mon, 15 Dec 2008 21:55:21 -0600
- Acceptlanguage: en-US
- Thread-topic: GRACol Paper classification
Hello Clark. Confusing isn't it!
The document you are referring to may also be known as GRACoLSpec2007errata.pdf. Get it at www.gracol.org/specification/GRACoLSpec2007errata.pdf If I may be so bold let me suggest you get a sharpie and cross out the premium column as it is not referenced in ISO 12647-2, from which Gracol was derived.
Just as paper weights can be completely meaningless when the basis weight and paper type (e.g. text or cover.....which eighty pounds are we talkin’ about willis?) is not taken into consideration, so can paper categories in terms of 1,2,3 when the foundation for the metric has not been clarified.
The paper industry uses a GE brightness meter to measure the percent reflectance at a standard single 457 nm wavelength.
http://www.internationalpaper.com/Paper/Paper Products/P_and_CP Stand Alone Pages/CP_and_IP Stand Alone Pages/Print_Producers_KC_B1.html
Depending on how bright the brightness or whiteness, paper is defined in a quality tier. See http://www.unisourcelink.com/paper/commercialprinting/pdf/HowtoQualifyWebandSheetPapers.pdf
Typically the higher the brightness the more money the sheet will sell for. Some "house" sheets are toted as having a number 3 price with a No 1 quality. (sigh).
ISO 124647-2 categorizes paper types: 1/2, 3, 4 & 5 based on the L*, a* and b* values. Please disregard the Tappi metrics and learn to speak ISO.
Your press operators are confusing No.1 with Type 1, so be careful with semantics. Gracol characterization data is based on ISO Type 1 with L* 95 a* 0 b* -2. As for the TAPPI rating? anyone? anyone care to tell us?
Not that you asked, but currently there is not a metric for describing the amount of optical brighteners, which largely affect the b* value as well as cyan and magenta hues. As an industry we can't begin to speak intelligently about brighteners and how to buy them or not buy them or how to print on them or measure them aside from avoiding them altogether. Its safe to say in many cases your spectro sees paper differently than you do. (sigh #2)
The densities you refer to are "PRE"2007 press control guidelines. Clark, please consider placing this chart in your recycle bin. Your guiding lights are the ISO 12647-2 2004 AMD 1 2007 CIElab aimpoints for KCMY are provided per paper types [1,2,3,4,5]. The G7 how-to has basically the same aimpoints; anyone who tells you differently is splitting hairs. Overprint colors are suggested too and I suggest you focus on those and let the CMY values fall where they may.
There is a sea of stocks and your path to finding the one you want is to measure them yourself. What you will find is that many sheets do not fall within the ISO parameters but are close to or closest to a specific category. Whereas Valuegloss/Pacesetter fits nicely within Type1, every uncoated sheet I could lay my spectro on was a far cry from Type4. You'll want to try your luck tweaking target values per section 6.4.1 of the G7 Amendments working draft. I can send you a spreadsheet offline to make this easy for you.
http://www.idealliance.org/g7global/howto/G7Amendment08_dh_3.pdf
I cannot offer any insight as to how the paper industry’s quality metrics correlate to ISO paper types. It is safe to say the industry will not eagerly assist you in finding the papers you are looking for, although they will eagerly take you P.O. Gradefinders wont help you. Mill websites wont help you, except on rare occasion. Your rep probably wont know what you are talking about. If he/she does, please send me a phone #. My approach was to measure every sheet within my budget and take note of the ones that have a legal gracol white point. The papers you mention were over budget so I did not measure them. My merchant could not assist. I asked. Your best friend in this endeavor is yourself and a spectrophotometer without filtration.
If you can budget for a tool such as SpotOn from AlderTech, you path to enlightenment will become shorter - not only for you but for your press operators, who will finally "get it" when they see how density correlates to CIElab aimpoints.
Good luck with all this. It isn't easy.
- Matt Louis
On 12/15/08 7:28 PM, "Clark Steve" <email@hidden> wrote:
I'm looking at a sheet called GRACol 2007 Print Characterization
Charts. There are columns for the paper type with rows for Screen
Ruling, TAC, Lab paper white, Lab for the primaries, and on down to
suggested SID and TVI etc. The column labeled "Premium text & cover"
puzzles me. It suggests possibly dropping the ruling to 150 lpi and a
TAC of 260% and considerably low SIDs. Is this for uncoated papers?
The word Premium is throwing me a little, but the TAC seems right for
uncoated.
A bigger question is how does one relate actual paper brands to these
columns, i.e. Where does Topkote Gloss fit in there, or Matrix Matte,
Endeavour Velvet, McKoy Silk???. Do the manufacturers supply any
information that lets you classify their papers to specific types with
respect to GRACol or ISO?
The reason this has become important to me is our pressroom has
started running their densities down. I discuss this chart and suggest
higher densities. They immediately point out that they are not running
number 1 or 2 sheets so the next column is this Premium test & cover
category with densities of 1.30, 1.15,1.15,.90.
Thanks for any and all information.
Clark
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