Testing Ink Samples On A Laboratory

[VinnyCordeiro]

First of all: this isn't my work. This guy on another forum made a series of tests with 5 different ink samples and found some very interesting results. He allowed crossposting it here.

I don't know if this is the right place for post. If not, I apologize and ask for a mod to place this on the right place.

Without further ado, here is the post:

 

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The Samples

Four samples were procured from CPTBadass and one was supplied by the author.

 

http://i.imgur.com/6dFS9lF.jpg

 

Noodler's Baystate Blue - a vibrant royal blue ink
Rohrer & Klingner Scabiosa - an iron gall ink
Noodler's North African Violet - an intense violet ink
Diamine Soft Mint - an ink that appeared turquoise or aqua in the bulk solution
Noodler's Polar Brown - a somewhat rust tinged brown ink

Upon receipt, the samples were transferred to 20mL plastic scintillation vials. The original containers' opening was too small to accomodate the probe used in the pH experiments.

1. Shake Tests

Method

Samples in scintillation vials were given a quick shake and observed for fluid and surface characteristics.

Results

InkObservations

Noodler's Baystate BlueInk left a thin layer coating the wall that persisted for a long time. This thin layer did not show any detail of the plastic surface. It produced bubbles.

Rohrer & Klingner ScabiosaInk left a very thin layer coating the wall that persisted for some time. The layer highlighted plastic imperfections of the bottle by contrast. It produced bubbles.

Noodler's North African VioletInk left a very thin layer coating the wall that persisted for some time. The layer highlighted some plastic imperfections of the bottle by contrast. It produced bubbles.

Diamine Soft MintInk did not coat walls. Preferred cohesion and formed small islands of liquid on the plastic surface. It produced NO bubbles.

Noodler's Polar BrownInk left a very thin layer coating the wall that persisted for a long time. The layer highlighted plastic imperfections of the bottle by contrast. It produced many/large bubbles. Bubbles appeared to grow over time.

Discussion

The surface coating indicates that there was interaction with the walls of the container. Since the plastic was either polyethylene or polypropylene, we expect the walls to be hydrophobic. The inks which wetted the surface well interacted with the plastic surface. Since bubbles were formed, we can assume that the interaction with the wall was due to surfactant in the ink reducing the surface energy allowing this prolonged contact. The lack of coating in the Diamine sample suggests that it is highly hydrophilic. The lack of bubbles suggests that no surfactant was added to the ink during manufacturing.

2. pH Test

Method

Samples were tested for hydrogen ion concentration using a Vernier pH probe connected to a computer running the logging software. The probe was calibrated immediately before the experiment with a pH 4.00 buffer standard (Fisher - methyl alcohol, formaldehyde, and potassium hydrogen phthalate) and a pH 10.00 buffer standard (Fisher - disodium EDTA dihydrate, potassium carbonate, potassium borate, potassium hydroxide). The lab temperature was 25C, and the standard pH did not need adjusted from the label value based on this temperature.

 

http://i.imgur.com/6TxgSml.jpg

 

Results

InkpH

Noodler's Baystate Blue3.97

Rohrer & Klingner Scabiosa2.33*

Noodler's North African Violet4.60

Diamine Soft Mint4.00

Noodler's Polar Brown8.78

 

Discussion

The majority of the inks were slightly acidic in nature, and the Polar Brown ink was slightly basic. The iron gall based ink was quite acidic. This ink pH is marked with an asterisk(*) since the pH was not stable. The value continually drifted downward, trending toward acidity. The value used here was the observed pH value after 15 minutes of attempted stabilization. After the experiments were complete, the pH probe was observed to be slightly discolored. To determine how this effected the results, the standards were measured with the discolored probe. The 4.00 buffer measured 3.74, and the 10.00 buffer measured 9.88. This indicates that the results are probably skewed downward by ~0.25 pH units. The results were not corrected for this error, since it would be difficult to quantify the error without much experimentation. The probe was cleaned by soaking in 2% nitric acid for 30 minutes. After this time, the probe was deemed 'clean' and returned to storage.

The results of this experiment should clear up a few misconceptions. Notably, none of the inks in this less than comprehensive test were pH neutral. Some sources discussed previously make claims based on the acid or base nature of inks based on brand. Clearly, this is not a wise assessment. The brand with three different inks in the test (Noodler's) showed a wide range of pH values. Some outside sources suggest that acidic inks may damage pens. Most of the inks tested were acidic. No metal based tests were performed in this experiment, but this author believes that the correlation between metal pitting and acid content of an ink may be spurious.

3. Solvent Tests

Method

In this test, a small quantity of ink was deposited onto a strip of printer paper (Staples Brand) and partially submerged in solvent. The ink was applied to the paper by smearing one or two drops from a disposable plastic pipette on the paper. All labels on the samples were written in pencil. The ink was allowed to dry then tested. Most strips were folded so they would stand and set in a petri dish with the testing solution for five minutes. These tests were broken up into aqueous, organic, and chlorinated solvent groups to prevent unwanted reactions.

 

http://i.imgur.com/XVVn0fT.jpg

 

The wet papers were then taped to a rail in the hood to dry.

 

http://i.imgur.com/fOlnOxV.jpg

 

One strip was tested under a 18.4 W long wave UV lamp for one hour. One strip was left as a control.

Results

 

http://i.imgur.com/hR77I2n.jpg

Control

The numbers represent the inks Noodler's Baystate Blue, Rohrer & Klingner Scabiosa, Noodler's North African Violet, Diamine Soft Mint, and Noodler's Polar Brown respectively. The inks were not applied evenly, and some spreading, especially in samples 3-5 was due to large drops. The Polar Brown ink naturally feathers a great deal on this paper, and the Scabiosa and North African Violet inks showed some feathering. The Soft Mint ink naturally spread, but did not show feathering.

 

http://i.imgur.com/nQvZdF8.jpg

Water

12345

minimal featheringfeatheringfeatheringspread and lossNo Change (NC)

 

http://i.imgur.com/kvAekUy.jpg

Ethanol

12345

upward driftsome upward spreadupward driftupward driftedge reddening

 

http://i.imgur.com/uxswnLc.jpg

Acetone

12345

some spreadNCfeatheringupward driftNC

 

http://i.imgur.com/zhoF7Di.jpg

Isopropanol

12345

upward driftsome featheringsome feathering/driftsome driftNC

 

http://i.imgur.com/WhnziWl.jpg

Toluene

 

12345

upward driftNCminor driftNCedge reddening

 

http://i.imgur.com/CspPjwX.jpg

Nitric Acid (~4%)

 

12345

gone, yellow edgealmost gone, blue edgealmost gone, green edgegoneNC

 

http://i.imgur.com/GDRZQs7.jpg

Hydrochloric Acid (~4%)

12345

gone, yellow edgealmost gone, blue edgealmost gone, green edgegone/upward driftedge reddening

 

http://i.imgur.com/xA20NoK.jpg

Dichloromethane

 

12345

upward driftfeatheringupward drift/featheringminor upward driftyellow color separation

 

http://i.imgur.com/PwQK9tk.jpg

UV Exposure

 

12345

NCNCNCNCNC

 

Discussion
There is a great deal of information to be learned from these tests. What we are looking at is actually a very rudimentary form of thin layer chromotography. The paper acts as a stationary phase and the solvent as a mobile phase. The mobile phase moves our eluent along the capillaries within the paper fiber matrix. If we let this go for a long time, we would see the individual components separate from each other. There are better methods to perform that experiment though, and it was not in the scope of this one. The goal of the test was to determine the stability of the ink when in contact with the solvents. In doing this, we can learn something about the character of the ink.

Different solvents have different polarities. The polarity of a molecule being the concentration of electrons on one side of an atom and exposed protons on the other side. We can relate these by a polarity index:

 

http://img.docstoccdn.com/thumb/orig/159941026.png

Since "like dissolves like" if something is moved or dissolved by more polar solvents, then the material must be polar. So we can see that the Diamine ink is more polar than the quite nonpolar Baystate Blue based on what different solvents do to it.

The Polar Brown ink interestingly slightly drifts in both polar and nonpolar solvents. If you look closely (probably not visible in pictures), you can see a yellow component separate out in nonpolar solvents and a red component separate out in polar solvents. These colors moving out of the bulk drop only slightly affect a color change in the brown.

I chose the two acids to test here on purpose. We would expect the HCl to react mostly as an acid, whereas the HNO3 would react as both an acid and a strong oxidizer. Since both of the acids had similar effects on the inks, we can see that none of the inks oxidize easily - which speaks well for the permanence of these inks.

Future tests would include solvents with polarity index of 0.

The lack of change due to UV light is good, though this author would like to point out that this was not a very strong source. Future tests should attempt to use more powerful sources such as a laser.

A. Errata

All solvents were obtained from Pharmaco Aaper with purity >99.5% except the nitric acid, which was obtained from Fisher.

All water used in the experiments was reagent grade, purified by reverse osmosis to resistance of >18Mohms.

I would like to thank CPTBadass again for his donations and my advisor for being out of town this week so I could do silly experiments like this without getting yelled at.

Thank you for reading, I would be happy to address any questions or comments you may have about this work.

 

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Link to the original post: https://geekhack.org/index.php?topic=59329.msg1831525#msg1831525

[DrDebG]

Very nice experiment. Prior to starting the experiment, what was your hypothesis? Did you prove your hypothesis? What are your conclusions? I realize that this was not your work, but I would really like to know your opinion of the results.

[VinnyCordeiro]

There was a previous discussion there (that I didn't mentioned, now I see) about ink pH. The test was to settle this discussion down, I believe. And we can see that the "always pH neutral" from Noodler's isn't quite true.

[amarjit]

great detailed experiments, thanks for sharing with us.

[DrDebG]

There was a previous discussion there (that I didn't mentioned, now I see) about ink pH. The test was to settle this discussion down, I believe. And we can see that the "always pH neutral" from Noodler's isn't quite true.

 

I would agree. Your tests showed that the four Noodler's inks aren't pH neutral. I appreciate all of the hard work that went into this experiment. Thank you, and please pass our thanks on to CPTBadass. It would be wonderful to repeat this experiment with other brands as well, completely blinded to the experimenter to reduce bias. And it would be really good to include a control (i.e. something known to be acidic, and another to be basic).

 

Are you and CPTBadass chemists?

[Oldtimer]

I wonder… Is this acidity detrimental to the pens, the paper, the hands, etc? Would this acidity account t for the odor or Noodler's inks, hum! 2.33 is highly acidic.

[VinnyCordeiro]

 

I would agree. Your tests showed that the four Noodler's inks aren't pH neutral. I appreciate all of the hard work that went into this experiment. Thank you, and please pass our thanks on to CPTBadass. It would be wonderful to repeat this experiment with other brands as well, completely blinded to the experimenter to reduce bias. And it would be really good to include a control (i.e. something known to be acidic, and another to be basic).

 

Are you and CPTBadass chemists?

 

First of all: this isn't my work. This guy on another forum made a series of tests with 5 different ink samples and found some very interesting results. He allowed crossposting it here.

 

I can't say about CPTBadass, but I'm for sure not a chemist. The last time I was in a chem lab was in high school, almost 20 years ago.

[mhosea]

There was a previous discussion there (that I didn't mentioned, now I see) about ink pH. The test was to settle this discussion down, I believe. And we can see that the "always pH neutral" from Noodler's isn't quite true.

It's certainly not literally true, but that is not a new revelation. We've had pH-meter readings done in the past.

 

https://www.fountainpennetwork.com/forum/topic/154941-checking-the-ph-of-inks/page-2?do=findComment&comment=1558048

https://www.fountainpennetwork.com/forum/topic/185342-ink-acidity-and-alkalinity/

 

It's not like you can use pH test paper, so everybody is using some kind of electronic probe device that must be calibrated and used properly. Nevertheless, the measurement on Baystate Blue is surprising because BSB is famously supposed to be alkaline, and I'm sure it has been measured as such independently in the past (not that I recall who did so). Suddenly it is supposedly not much different from the typical pH for a blue ink of western origin? There's a mystery afoot, boys. The issue of measurement calibration has been addressed in the study, but the issue sample integrity does concern me. Some inks of this nature have been observed to behave differently over time, such as either drying normally or exhibiting very long dry times. The mechanism for that is unknown. I have always supposed it to be primarily a matter of evaporation of water in the feed (having observed much longer dry times in ink written from the pen normally and ink taken directly from the converter), but perhaps there is more to it, something that might affect pH in a profound way. At any rate, a small quantity of ink sloshing around in a much larger container with air, perhaps being exposed to heating and cooling cycles, might well test differently than something straight out of a fresh bottle.

 

As an aside, Waterman inks I think came up in the blog and mentioned as "safe", but Waterman inks weren't tested here. In the past Havana Brown has come out neutral, but Blue came up as relatively acidic (below 4), and Purple came up as highly acidic. Around the 3-5 range is where most of them seem to fall.

 

I don't personally think pH is a good indicator of pen safety, except as regards pens with plated metal at the end of the grip section which might be subject to corrosion if the plating begins to fail.

[VinnyCordeiro]

As an aside, Waterman inks I think came up in the blog and mentioned as "safe", but Waterman inks weren't tested here. In the past Havana Brown has come out neutral, but Blue came up as relatively acidic (below 4), and Purple came up as highly acidic. Around the 3-5 range is where most of them seem to fall.

 

This other guy made some more tests, including a Waterman sample: https://www.reddit.com/r/fountainpens/comments/3h494k/ph_testing_of_various_noodlers_waterman_and/

 

I agree with you when you say that pH alone isn't a good indicator of pen safety, but it is a parameter that can be measured and compared. Further chemical testing would be necessary for better results/conclusions.

[mhosea]

This other guy made some more tests, including a Waterman sample: https://www.reddit.com/r/fountainpens/comments/3h494k/ph_testing_of_various_noodlers_waterman_and/

OK, that helps a lot. Still mysterious, though.

[Brianm_14]

Two thoughts, suggestions perhaps. When I was investigating mammalian gastric juices, I always found it interesting to conduct old-fashioned biuret titrations with standardized acid and base. Quantitatively determines the amount of acid or base present in the sample. This can also help us understand the buffering capacity and pH stability of these inks. Sorry I don't have such analytic capacities at this time.

 

Might have been nice to run one or two controls as well. One might have been a simple well-characterized dye, such as eosin or methylene blue.

 

However, thanks for the work and the report, and I know how it is when your "forbidden experiments" must be promptly carried out under duress by mice working when the cat is absent -and I've been both a mouse and a cat!

[e-beth]

What I want to know is, how much did the analyst's blood pressure increase when they realized they had stained the probe on the pH meter? Those things ain't cheap.

 

Another interesting test would have been to use different papers in the chromatography tests (Rhodia, Clairefontaine, etc.).

[cybaea]

Fascinating! Thanks for sharing and please do keep us informed of any other experiments you may do

[amberleadavis]

Thank you for sharing. The tests and the analysis took a tremendous amount of time and effort. We really appreciate it.

 

I can tell you that with more time exposed to light, BSB and NAV completely disappear.