Digital BW, The Print

If you thought you had some issues, you would first want to isolate out conditions that might be contributing to your perception such as paper variation, humidity and temp, printer condition (whether temp or permanent), and the delivery system (cart problems or CIS problems.) If you use bottles to store our inks that are not of our supply then you might isolate that out as well (cheap Chinese plastics often are not inert.)

Then I suppose you could bench them against a standard. The easiest is to fill a fresh cart with ink in a clean desktop printer and after insuring that the printer is passing this new ink fully, to measure the 60 or 80% patch of a QTR target. But, I caution you on this easy method. We tried to see if an inkjet printer could actually be used as a quality control check for L*a*b* and after 30 days of an experiment in which we produced QTR Epson Ultrachrome K3 density examples and QTR Piezography Special Edition K7 density examples (twice a day) on printers which were being used daily to produce samples - we concluded that the variation swings are too great to use a printer as a measuring device if a tight spec is required. With these particular inks (we think OEM was same) ((we knew the SPED was same batch)) and the papers were same batch - we believe it is the simplicity of environmental conditions such as temp and rH that are more sensitive than we previously believed. We sometimes wonder about the actual piezo crystal and if it is subject to fluctuations.

I believe that the only way is by draw down sample. If it is not obvious to you that something is amiss and you can't isolate any one specific cause, or that isolating a condition produces other unexpected results - then you stop chasing conditions and simply measure the ink itself.

In this case, the investment of a system that automates a small draw-down bar so that it isolates human fluctuations in pressure, etc.. can be used as long as you have the specifications for a similar system on a specific test media. This is how its controlled in the laboratory. Of course the measuring device to sample the Lab color and density must be consistent with the device used in the laboratory and for which you have specs.

So - I would first try and isolate what it is you think you perceive (if its that a particular paper you love is now printing differently), and try to attempt to recreate the issue on a different condition (compare examples of another media type between new and old). This might rule out media. 

A poor man's draw down bar is a drop of ink on a semi-gloss paper and a razor blade. The paper begins to absorb the ink but the squeegeing of the ink with the razor across the paper will produce a portion of very consistent density and tone that you can then measure. But it will be with its own variation. 

We generally do this as a fast QC when we're bottling to isolate a 15L jug just as a precaution. It's not exact but it reveals quickly.

I hope somewhere in this long answer will be a method you can adopt.

Jon Cone
Piezography

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, t.ritz@... wrote:
> 
> Jon, how can I tell if my batch of K7 Selenium inks has an issue?
> 
> Thanks.
> 
> Terry.
>