There are dedicated sites for testing ink. Why is that so important? How can you test your own ink?
People who test inks are either salesmen or penofiles
It takes several years for a regular person to finish 50 ml of ink. Using multiple inks with the same pen is not an issue, but rinsing the pen between inks is a headache. Once we buy our three or six initial inks, it takes several years before we really need more. Moreover, very few people will ever need more than six different fountain pens at the same time. In other words, if you do not rely on cartridges and use large bottles, you will buy inks maybe on Christmas.
Your chances of getting ink samples to try are also not very high unless you are a blogger, a collector, or own a store. After all, each ink bottle starts at ten dollars and can easily go to a hundred dollars for limited edition ink with the shipment. Shipment is the biggest issue with ink: if you cannot find it in your local store, the shipment may be more expensive than the ink and it can be stopped by customs.
In other words, if you do not sell pens, review pens or admire pens, you will not spend your time and money studying inks. Luckily, there are experts who will do that for us.
Splash test
If you are not a penofile, you do not really know the other qualities of the ink. The only thing you want to see is a huge splash of ink on paper and the colors the splash takes. Bloggers are more than happy to provide these images. They look really good in their blogs.
The splash test colors are misguiding. Wet ink looks better than dry ink, and often is photographed before it dries out to see the sheen. You are not likely to see the entire palette of colors no matter how you use your ink.
Writing test
Instead of being mesmerized by splash nuances, watch long tests written with the pen using medium nib. By the time a page of text is finished the ink is alrady dry, maybe except for the last line. This is what you are likely to get unless you use special calligraphy tools. The colors in written text are very different from the splashes, and often much more uniform. With fine nibs you will see even less variations. What we see is more shadowing (saturation) than anything else, as the pressure on the pen is lower in some parts of the line. Occasionally we will see skips, but not in quality pens and inks.
Many bloggers also draw beautiful floral patterns with their inks. The ink is thoroughly diluted by water for most part, yet on the outlines it is pretty saturated. If you doodle, this is what your doodles will inspire to look like. We do not doodle with ten colors. All except cartoonists are not likely to use more than three inks per drawing. And we will not see all the wonderful patterns of splashes: good inks are pretty homogenous.
Now that you understand the color you are buying, you have dozens of manufacturers to choose from. Each with slightly different qualities. And this is where the ink tests get interesting.
The most important quality: drying time
I think that the most important quality of any ink is its drying time. Before you buy ink, consider how much do you want to wait for this particular ink to dry. Waiting for the ink to dry can be pleasant if you practice calligraphy or write a diary. It is an acceptable sacrifice if you are doodling. Probably it is less acceptable in a highly stressful business environment. You can use a blotter if you absolutely have to, but is it the experience you want?
Drying time depends on ink, nib size, and paper. It is usually tested on very smooth paper by bloggers. Your personal experience may be different. Bloggers draw a grid of several rows of vertical lines. Then they measure time, and every couple of seconds they try to smudge the next row. The first row after a second often is quite smudged but after 30 seconds almost all inks dry.
While bloggers may say that the drying time in their test is whopping 15 seconds for Pilot iroshizuku, I use the ink all the time and it dries almost instantly.
Water resistance
Usually, you want some medium level of water resistance. An example would be Papier Plume inks like Iron Lace or Kaweco inks. I read about these inks but did not have a chance to use them.
One exposes a dry grid of horizontal and vertical lines to humidity and measures the result. It is called water drip test. Higher level of water resistance
Pigment-based inks contain tiny particles of pigment that float around in the ink, examples include Sailor Pigmented and Rohrer and Klingner SketchInks. These inks in general are more water-resistant than dye-based inks and generally dry faster too, but they also tend to be harder on pens since the tiny pigment particles can clog your pen over time.
To be honest, this quality is sought after by artists and people who run archives. Most of us have no plans of exposing our pages to liquids. All of the inks I love and use have low water resistance.
The issue is: if you use medium quality paper and broad nib with inks of higher water resistance, you are likely to see no feathering. This is actually a big deal.
Subjective qualities
Some people love an extremely smooth feel of the nib on paper. People buy quality paper and #6 gold Jowo nibs to feel the pen gliding. The feeling is described as velvety. Some companies help that feel adding lubricants. Parker inks are most famous for their lubricity. Other penofiles mention Sailor and Diamine inks.
Another common issue is nice flow of the ink. The ink flow needs to be well-behaved especially with flexible nibs like Pilot FA and Noodler Ahab. Not every ink has a consistent flow. The ink may temporarily dry out on the nib, causing strange skips. It may also splash from the nib if the viscosity is low.
Clogging of your feed is another pretty subjective quality. There is no clear test for it, yet it can happen. Especially if the ink is old and dry and water-resistant.
These qualities are hard to measure and we have to rely on subjective judgment rather than photos.
Swabs
Rather than doing saturated splashes, good blogger also do swaps. They test various levels of dilution of ink with water. Swaps are very important for artists who tend to use some inks like water colors. The result is very delicate and beautiful, and shows various levels of shading some inks have.
Other inks do not behave well in dilution and generate very strange patterns. When you actually write with a broad nib, you might be looking for those specific patterns in your line, but when you are painting with ink you probably want to avoid those patterns.
The swabs look very good on photos, and allow to choose the best variations within the line and the most well-behaved inks for dilutition. You may end up buying two very different inks of roughly the same color used with equally broad nibs. So you are likely to spend more, but spend wisely.
Chromatoscopy
Next you want to see how pure is your ink. Most inks will show a combination of the main color, and some underlying deeper and heavier die. To see that, a very porous paper like coffee filter is used with lots of water. Lighter dies splash out creating wonderful comet-like tails. Heavier dies will not move so easily, and you will see the underbelly of your ink.
The chromatoscopy results are very beautiful, and once you selected your ink you will understand it better. Its like wine conessuers discussing their wines. You will start to see extra colors in your ink. Nobody but you will see that in your text or drawings.
I would say that chromatoscopy is very impressive, possibly hypnotizing but not very useful for most of us.
Mixing inks
Some people enjoy creating their own inks using some sort of secret recipes. Many things can go wrong in the process, but if all is successful you will have your own unique ink.
You might want to mix some similar well-behaved inks of the same manufacturer. To do that you usually take two related colors like green and blue or ruby and orange. Then you start minixng in different proportions, thoroughly testing each proportion.
First you need to see that there are no particles. Then you need to see that the result is satisfactory. You will probably not do the process with the cheapest inks or with the fancy vibrant colors, but with some mid-range ink.
Notice that you are likely to be the only person admiring the complexity and perfection of your color, generated after a week of thorough testing. For everybody else it will look very much like a standard color of some big manufactarer.
Lubricating inks
There are three ways common people lubricate inks. Some add water, some add dish soap and some add glycerine.
Dish soap is a bit hard to control and produce consistent results. It can increase the drying time and feathering. The flow rate may get reduced. Not the best choice for a lubricant….
Water may reduce drying time and feathering, and most inks are water based. The question is: how saturated you want your ink to be? Also, you directly effect the so called humectants that affect the wetness of your ink. Reduced lubricity is just a side-effect.
Glycerung may increase drying times and reduce water resistance, but the lubricity will increase almos directly. If you want smoother, wetter ink consider this option.
This is about everything I know about the subject. Now it is time to hit the blog and check the inks you are going to buy.