The quest for the perfect inkset - a scientific ink test

nertog

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The quest for the perfect inkset

After a long love-hate relation with my old Canon IP8500 I decided it was time for an upgrade. I wanted a machine that could take anything I throw at it and print it with perfect quality. A bit of market research revealed that the new Epson R3000 would fit the bill. It's well built, prints on a wide range of media and the piezo printhead basically prints everything that's liquid. The problem: what would I feed it with?

The R3000 uses the K3 inkset with Vivid Magenta ink. This pricey inkset boasts a large colour gamut, eliminates bronzing and the pigments offer excellent fade resistance. There are 2 problems however: the performance on glossy papers and, of course, the price. I decided that the gloss difference problem could be solved by using dye inks. Dye inks look excellent on glossy papers, but they are very fragile and short lived. I didn't want to choose between gloss and fade resistance so I decided to use a second inkset with pigment inks...and so the long search for 2 perfect inksets started. After contacting many manufacturers and asking about the ink gamut, gloss and fade resistance I found out that none of them has any data to back up their claims. Every single manufacturer and reseller claims to sell the glossiest, most colourful and most fade resistant ink on the market. Rrrright. Time to set up my own test.

I wanted to measure mainly 2 things: the chroma of the inks and durability (= fade resistance). The chroma of each of the CMY colours determines the gamut volume of the inkset. Chroma is easily measured by taking a spectrograph and checking the pure ink colours. Measuring durability is not that easy. My past experience with dye inks learned me that the main problem is not the light that's fading the colours, but ozone gas. Ozone is a very strong oxidizer and this causes a photochemical reaction that fades away the colour of the ink. Oxygen does the same thing, but at a much slower rate. I decided that the ozone fade rate would be a good indicator of the molecular strength of the dye and pigment inks.

The picture below shows the ozone test chamber. It included a small electric ozone generator and fan to provide some circulation inside the glass chamber.



I acquired 6 different inksets: 2 dye based ones, 3 based on pigments and 1 dye-pigment hybrid inkset. Based on past experiences I wanted to test 2 excellent dye inks: OCP CLI-8 and Hobbicolors CLI-8 inks. The chosen pigment inksets are an Inkrepublic IRK4 nano, Inkjetfly IMA24/36 V3 and a Pemla EDI Vivid magenta set. The hybrid inkset is manufactured by Pemla as well. Each ink was swabbed on Sihl 280g glossy microporous paper using a saturated q-tip. I made sure I used the maximum amount of ink on the paper without causing overinking issues. Both a test and a control swab of each ink were made. After a drying time both strips were measured using an I1 spectrophotometer. Here is how the strips looked like before entering the ozone chamber of death:





People who have a calibrated wide gamut monitor can have a look at the images below, made with a colour calibrated camera in a viewing booth using a D65 illuminant:





After the initial measurements: the ozone test.

Results after 7 hours:






The dye inks are suffering. Note that the cyan ink is the weakest link in any dye inkset. OCP has a clearly stronger cyan dye.

After 16 hours:





The dyes are gone. OCP's cyan clearly wins, but hobbicolors has a stronger black, magenta and yellow. Look closely and you'll see the the pigments are giving in as well: light cyan, cyan, light magenta and magenta pigment of all 3 manufacturers shows signs of fading! Yellow, all grays and both blacks are very strong. The hybrid Pemla Endurance inkset sits inbetween the dyes and pigments.

Now, what do the measurements say? In the link below you can download a spreadsheet with all the acquired data. I measured LAB values before and after the test and calculated the chroma of each ink. The higher the chroma, the more intense the colour of that specific ink. The average CMY chroma should give an idea about the gamut volume. The second tab shows the same ink swabs after the ozone test.

http://www.2shared.com/document/0Z1YD8fh/Comparison.html

So, easy now to assemble 2 perfect inksets huh? Not really. For the dye inks it's easy. Take the ones with the highest chroma and there you go. Coincidence or not, these inks also have the best fade resistance. The pigment inkset is another question. The hybrid inkset is a no brainer: bad chroma and not very fade resistant..except...the black ink is excellent! With an L value of 2.xx this is the blacked ink I have ever seen. It's very fade resistant as well. The other inkset all have their strengths and weaknesses: Inkjetfly has a strong yellow, but the blacks are weak. The inkrepublic ink has a very strong magenta and nice deep blacks. Not a bad choice at all! However, and this is not visible in the test: the light black suffers from bronzing. The Pemla EDI inkset has by far the best gloss but is a little bit weaker in chroma. Based on the measured values you can mix your own inkset. I believe that all 3 of the pigment inksets use the same cyan and yellow pigment. They do use different magenta and black ones. I was a bit surprised by the sensitivity to ozone, but all 3 of them seem to be equally sensitive. At leasts noone is using dyes in their pigment sets.

After all this testing I remain with 1 big question: people who used these 3 pigment inksets in their printer reported quite large differences in gamut volume using the sqme paper and printer. Inkjetfly has the largest gamut, Pemla seems to have the smallest one. I doubt that such small chroma differences of the CMY colours can cause such a large gamut difference. I noticed, however, that the density of the light cyan and light magenta inks is very different in each of these 3 inkset: Inkrepublic uses a light cyan of almost the same density as it's cyan and inkjetfly uses a very dense light magenta. I can imagine this has it's influence on the Epson ABW mode but...

what is the influence of the light cyan density and light magenta density on the overall colour gamut? If anyone has any ideas or opinions I would love to hear them.

I hope some of you can use this report and data to find their perfect inkset! You probably realised I didn't give any print permanence data in years. The simple reason is that I had no means of measuring the ozone concentration in the chamber. One fact: a print with OCP dye ink on the same paper shows visible fading after 3 months, unframed, displayed in a normal living room.

Greets,
Wim

All measurement data, pictures and report: http://www.2shared.com/file/FnbRtdK0/post.html
 

jkhes

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I can't see the pictures in your message. "domain unregistered" :(
 

Redbrickman

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I have one question.

Is ozone the only thing that fades ink?
 

nertog

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jkhes said:
I can't see the pictures in your message. "domain unregistered" :(
They are hosted by Imageshack. Works fine here. Anyone else having the same issue?
 

nertog

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Redbrickman said:
I have one question.

Is ozone the only thing that fades ink?
No, ozone is just one of the problems. Short wavelength light (intense blue and uv light) are also damaging pigment and dye inks. Ozone testing was just easier and I believe that it shows the relative fade resistance of the ink. I think a fade resistant ink will be more resistant to both light and ozone.
 

Grandad35

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Ozone and UV fading are very different, and one cannot be inferred from the other.
 

slocumeddie

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What was the ozone concentration in the "bell jar" in pphm or ppb, and how does it relate to real world storage or exhibition conditions ? :hu
 

nertog

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slocumeddie said:
What was the ozone concentration in the "bell jar" in pphm or ppb, and how does it relate to real world storage or exhibition conditions ? :hu
No, as I couldn't measure the ozone concentration there is no way of extrapolating this to a real life situation. You can compare results inbetween the inks themselves though.

I know ozone and light fading are totally different mechanisms. This test is just an ozone test, but I feel it does show the strength of the dye molecules and pigment particles.

For me the colorimetric measurements of the inks were more interesting. There are huge differences in magenta inks and even bigger differences in the densities of light cyan and light magenta. I wonder which impact this has?
 

ThrillaMozilla

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Good for you. Thanks for doing the test.

I notice that applying ink by hand is MUCH easier than using a printer, and yet you can still compare fading of inks in this way, even if the results are not as accurate or precise as could be obtained with a printer. I wish more people would do color swab tests of this sort, because these tests, even if they are not exquisitely accurate, are vastly preferable to no information at all.

There are some things I don't understand, though.
1. What are the vertical stripes at 0 hours? This is seen even in the controls. Why?

2. The results show that part of each image has been masked, but the picture of the bell jar doesn't show this. And similar masking is seen in the controls. I don't really know what's going on.

Pigment inks are harder to apply uniformly. It would have been much easier to see changes if you had moved the swab horizontally instead of vertically.

I am skeptical of the color or saturation comparisons between inks, however. The ink smears are quite inhomogeneous, so there are large errors in any measurement. Furthermore, it's doubtful whether the amount and color of ink that you get is entirely representative of what the printer delivers.
 

nertog

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Using a printer is indeed impossible. Without a rip you cannot control which inks are used for which colour.

The vertical stripes you see is just masking tape used to attach the cards to the glass jar. It also gave me a way to position the I1 so that I could ready the same patch for each measurement.

I am quite convinced that the colorimetric measurements are ok. I tried to put down the maximum amount of ink that the paper would accept and measured in a spots that were not obviously affected by swabbing artifacts. In real life it's easier than it sounds.

I still wonder which effect the differences in density of these inks have on the overall colour gamut.
 
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