We have taken a combination of two posts on CEO Jim Raffel’s personal blog to discuss measuring inkjet proofs. They has been repurposed for this blog. If interested, you can read the original posts from July 27, 2005, and March 9, 2006.
Before we begin, understand that our frame of reference on this post stems from users of our software who rely upon density and TVI as process control measurements for inkjet proof production.
The shifts can make TVI meaningless
Far too many times, we have seen the density and TVI values stay within tolerance on an inkjet proof and yet the Delta E shifts can be huge. In the past, we have graphed the spectral responses of the red, green, blue and visual filters used in graphic arts densitometry. Those filter responses are specifically designed to address the spectral response of process cyan, magenta, yellow and black. We have also seen graphs which compare the spectral response of offset printing inks with typical inkjet inks.
But if you want to measure it anyway, hang it out to dry
However, whether we like it or not, TVI is still being measured on inkjet proofs in the print industry. We realize it and understand it. One of the more common questions we are asked is how long an inkjet proof should be left to dry before it’s measured.
While there is not a single correct answer to that question, we have some basic guidelines from the field. Obviously, before following our suggestions, it is very important to check with the manufacturer of the paper and ink that you are utilizing to print your proofs. They should know how long a dwell time is necessary before the proof is sufficiently dry that no more color shifting is occurring.
Our general rule of thumb when we go in the field to assist our customers in setting a baseline or gold standard is to wait 30 minutes after the proof has finished printing before measuring it. We vary this a bit depending on the ink technology (pigment vs. dye), but it seems to be a pretty good rule of thumb.
Now we recognize that waiting 30 minutes to measure every proof may not be practical, but we are talking about establishing the baseline or gold standard proofs right now. Once you have that down, you can make another proof to test for the optimum dry time for measurement of production proofs. Starting five minutes after a proof has finished printing, measure the control strip every five minutes for half an hour.
Bring on the software
Using the software you utilized to measure the proof, take a look at the trend line analysis of the Delta E shift over the next 30 minutes. You should be able to see a clear place where the shift levels off. Again, depending upon your environment (temperature and humidity) and proof type (pigment vs. dye), this could be at 10 minutes or 20 minutes.
This is a good strategy to figure out how long to wait in order to get accurate proof verification measurements.
For additional reading on this subject, we liked this post from The Print Guide which details how to extend the life of the color integrity of your inkjet proofs. If you have any best practices, we’d love to hear about them!