Thursday, July 2, 2015

Measuring nib flexibility

Once buyers started bidding up pens with flexible nibs to unprecedented levels, sellers began to cash in by overstating the flexibility of their wares (related posts here and here). This has in turn renewed interest in establishing some sort of grading scale for flexibility.

Establishing any sort of standardized flex grading system will not be easy. At minimum, there would have to be one scale indicating the range of line width variation, and another scale indicating how much pressure is required to make the nib open up. Unfortunately, I can think of no practical way to prevent the first scale from being subjective and inconsistent. Maximum line width for a given nib will differ greatly depending upon whether it is pushed to its short-term limits or kept within its safe range for sustainable long-term use. And while photos can show when a nib is being pushed far into the danger zone, in most cases there is a large grey area which one has to navigate by feel, not by eye.

The second scale is another story. Instead of continuing to rely upon poorly defined labels such as "easy flex", "full flex", "superflex", and the odious "wet noodle", correlating the force applied to a nib and the resulting deflection would provide a precise and uniform method of grading.

Two versions of this approach have been proposed in recent years. The first, explained in this YouTube video, entails measuring the pressure required to make the nib open up to its maximum safe width. Quite aside from the issue noted above of determining that width, this method also fails to provide figures for comparison that are truly comparable. How is one to compare a nib that writes a 2 mm line with 250 grams of pressure with another that writes a 2.2 mm line with 280 grams of pressure? Perhaps both require the same pressure to reach 2 mm, but one just happened to have been pushed a bit harder. But there's no telling, since the measurements were not made at a standard angle of deflection.

Addressing this problem, another method fixes the nib opening at a standard figure of 1 mm, further specifying an angle of 45 degrees between pen and paper. This is a definite step forward, though it is still not as exact or comprehensive as might be desired. As a practical matter, it is more than a little awkward to press a pen down on a digital scale, holding it at exactly 45 degrees, gradually increasing pressure until the tines are exactly 1 mm apart at the tip, and simultaneously noting the scale's reading. Furthermore, if one were to graph nib opening as a function of force applied, the resulting curve could vary considerably from nib to nib -- two nibs requiring identical pressure to open to 1 mm could well require substantially different amounts of pressure to open to 0.5 mm, or to 1.5 mm. Finally, 1 mm may be more than is safe for some nibs, especially smaller ones.

For informal use, the 1 mm method is approximate but simple, requiring only the absolute minimum of equipment. With only a little more work, however, much better measurements are possible. The pen holding apparatus shown below was thrown together using scrap wood and miscellaneous hardware. The digital scale is a cheap Harbor Freight unit, with the nib tip resting on a square of sheet acrylic. The pen is clamped between guide rails set at 45 degrees, and pressure on the nib can be varied by hanging weights (not shown) on the pivoted support arm.


This setup, along with a measuring magnifier, makes it easy to determine the exact pressure required to achieve a 1 mm opening. Even better, it allows for a much more complete picture of a nib's performance. For example, instead of using nib opening as the benchmark and then determining the pressure required, pressure can be used as the benchmark and the resulting line width measured. This can then be repeated with multiple pressure settings -- 100, 200, and 300 grams would cover the essential range.


Over the next week or so I will record and report measurement results for various pens, including some dip pen nibs favored by calligraphers for their flexibility. The latter should offer an invaluable benchmark. I will also start to report test results for flex nib pens I list on eBay, which may push other sellers to provide similar data. [Very belated followup post here]

ADDENDUM: Antonis Zavaliangos commented on the issue of dealing with friction -- in particular, frictional resistance to the spreading of the tines. While the use of an acrylic surface will reduce that friction, my preferred method (as planned) is to adjust the pressure to a convenient benchmark with the nib on the acrylic -- 100g, say -- then to ink the nib, put a sheet of paper over the acrylic, set the nib on the paper, and pull the paper out from under the nib. That way the nib will have the opportunity to open up fully, as it might not in a static test. It will also be much easier and more accurate to measure the resulting line's width than to measure the gap between the tines at the very tip.


FURTHER NOTES: Many comments on this proposal have focused on what it does not measure, rather than what it does. Excepts from some of my responses at FPN follow:
I have no illusions about the possibility of reducing the full experience of using a given flexible nib to numbers. It would be like trying to quantify a ballet performance, or the experience of consuming food. Such experiences can be expertly (if subjectively) described, but they cannot be meaningfully analyzed by being broken down to a series of objectively measurable data points.

All I am proposing is to measure one aspect of a flexible nib's physical characteristics, one key aspect that happens to be objectively measurable. The full expressiveness and fluidity of dancers you will have to judge by eye; but if you know that one can't jump more than a foot off the floor, it's a pretty good indication that the rest of the performance is likely to be substandard as well.

. . . there are certain vintage steel dip pen nibs that were turned out in the millions and which are still in plentiful supply. The scale of manufacture was enormous, and the consistency was excellent. Certain types are particularly prized by calligraphers for their flexibility, and since they are so much a known quantity, they will offer excellent benchmarks for any quantitative grading system.

As I noted in my blog post, while measuring how much force is required to produce a given degree of deflection is straightforward, determining the maximum safe degree of deflection is quite another matter. This is inevitably going to be a judgment call, and highly subjective.
If we were dealing with large numbers of absolutely identical nibs, one could test a small number to destruction to establish the range of flex safe for sustained usage. But since we are dealing with individual nibs, each of which is different, we are stuck relying upon "feel" and experience. 

1 comment:

Brian Leair said...

This is a great idea and a concrete proposal for an objective means to characterize flexibility. It's a tough problem.

Another challenge is how another important aspect of how a flex pens write is its "snapback" or responsiveness. That is, after one flexes to make a wider stroke, how quickly do the tines close back and return to their non-flexed position. In some writing samples you can sometimes see this, but I'm certain some writing samples are done that don't represent what any real writing would ever do to get the huge swells.

In the end, each seller varies in how much they hype and try to mislead in order to get that "feeding frenzy" sale. I think some are blatantly dishonest. I've had the best luck for flex pens by going to a handful of sellers that others in the pen community have recommended.

Great post.