Details of ink dots on paper

[Grandad35]

I had a chance to look at some printed images under a good microscope, and I thought that others might also be interested. This image shows the ink "dots" printed for a thin, light band (a section of chain-link fence in the distance). It was necessary to select a light area, since the individual color dots could not be seen when a darker section was selected. Note the seemingly random pattern of the dots used to break up any repeating pattern that our eyes might pick up.

The full width of this image is about 700 microns (0.03"), and the "dots" are in the range of 50-70 microns (2-3 mils) in diameter. Note that the yellow dots appear to be slightly larger that the PM and PC dots. This illustrates that the colors that we see depend not only on how the inks color the paper, but also on how wide the ink spreads when it hits the paper. These dots were generated on a 2 pl printer, and a 1 pl printer should produce about 30% smaller dots (assuming that the ink is absorbed to the same depth for both dots).

I also took this opportunity to look at a conventional photo print as seen below. This technology also creates small areas of colored organic dyes in the paper, but the "dots" are very much smaller than with an inkjet. It will take a 10 femtoliter inkjet print head to give the same dot size as a conventional print.

 

[Nifty]

Grandad, excellent post!!

It is interesting how imperfectly shaped and sized the dots look. I would expect more consistent shapes and sizes.

The magnification on the two images aren't the same are they? If yes, then I'm amazed that the prints I receive from my printer look as good as they do compared to prints from the "store".

By the way, how did you acquire the image? Did you stick a camera in the peephole of the microscope, or was it projected onto a screen?

 

[Grandad35]

Rob,

I'm not surprised at the variation in the dot size when you consider:
1. This printer uses 768 individual nozzles for each color, so each of these dots probably came from a different nozzle.
2. Given the small size of the nozzles and the manufacturing cost per nozzle (a replacement head sells for about 1.5 cents per nozzle, so the manufacturing cost for one nozzle must be well under 0.5 cents), it would not be surprising if the individual nozzles behaved differently.
3. Nucleating a small steam bubble to eject a 16 micron diameter ink bubble is a process that I would expect to have some random variation.
4. The final size of the ink dot is also very dependent on the uniformity of the (in this case) nanoporous coating on the paper. I don't know any manufacturing details for this coating, but I wouldn't be surprised to find variations that would have a major impact on the final printed dot size.

I should have stated that the magnifications for the two images are the same. You can see something of the inkjet dot pattern with a magnifying glass, but obviously not in the same detail as with a microscope. Even so, when viewed at any reasonable distance, our eyes do not have the ability to see details this small, so the dots blend into a continuous image. Your pet eagle might disagree.

I said that this was a "good" microscope (it cost about $20,000 10 years ago). It has a Hitachi 640x480 color video camera that gets the same image as the eyepieces, and uses a frame capture card in a PC to capture a single video frame on demand. Actually, the biggest problem was that the standard reflected light used to illuminate the subject completely washed out the colors. We had to use "dark field" illumination, where the illumination light is brought in through the lens in such a way that it shines on the subject from a very shallow angle.

 

[SpideRMaN]

I know this is a very old topic but the link to the images is dead and am curious to see them.

@Grandad35
Do you still have the images please ?

 

[Grandad35]

I know this is a very old topic but the link to the images is dead and am curious to see them.

@Grandad35
Do you still have the images please ?

No, I didn't keep a copy as they are hosted on the forum. I sent a PM to Rob to get his input.

 

[Grandad35]

SpideRMaN,

Rob informed me that a number of files seem to be missing from the server, and that they have been missing long enough that his archive backups don't have them, either. Unfortunately, I didn't keep a copy either. If Rob finds them somewhere, I'll let you know.

 

[Nifty]

Ya, it's the most odd thing! It isn't all the files, but just a select few and I can't find any commonalities between the files or when they went missing. Sorry about that.

I'll keep digging and hopefully find another backup somewhere. This is really bothering me since I'm very anal about backups and missing files!!!

 

[SpideRMaN]

No Problem.

Thanks for your efforts I was curious cos I have never seen a microscopic photo of the ink droplets

 

[Grandad35]

Good news - Rob was able to locate a backup copy and restore the images.

 

[SpideRMaN]

Good Job Rob !!

He managed to recover pics in other topics too

Thank You