Tuesday, December 28, 2010

Tungsten Density Experiment

Tungsten beads are popular in fly tying circles, but they are subject to never ending discussions about their quality (or rather cost vs. quality ratio). The discussion usually ends up that the cheap beads are sure to be Chinese (with implication that nothing good ever came from China, with possible exceptions of paper currency, gunpowder, tonkin cane and cheap takeaway food).

By a fortunate coincidence I received a significant order for tungsten beadheaded flies and discovered very competetively priced beadheads on a Polish internet site (www.taimen.com) in a single week. This led to me obtaining enough beadheads to be able to measure their density directly.

I used a method very similar to the one employed by Mr. Archimedes to determine the purity of a golden crown for Hiero II of Syracuse. I measured 10 ml water in a beaker and poured enough 3.3 mm beads for the water level to rise to 20 ml. It took 755 beads to acheive that.

The second step was to let the beads dry and weight them. The 755 beads weighted 188.5 grams, i.e. the observed density of my beads was 18.85 gr/cm³.

The result came as a pleasant suprise, as the observed density was very close to the density of pure Tungsten (19.25 gr/cm³) and significantly above both Brass (around 9 gr/cm³, depending on alloy) and Lead (11.34 gr/cm³). Lower density than pure tungsten was to be expected due to technology used to make the beads and the fact that the beads are gold (i.e. brass) plated.

My conclusion therefore was that the Taimen beads are perfectly OK to use; to get better ballast I would have to resort to pure gold (density 19.30 gr/cm³) or platinum (density 21.41 gr/cm³), both of which are highly impractical for fishing use.

It also led me to think that some of the disparaging of cheap "Chinese" beads by fly shop proprietors might be due to other reasons than quality of the product.