Properties of Plectra Material
Acetal / Delrin® / Celcon® / Birds' Quill
While traditionally plectra were made from birds' quill, the plastic acetal has become the
material of choice due to its longevity. Acetal is available as homopolymer and copolymer and in various grades for different applications.
Acetal in its various forms is marketed under brand names like delrin, celcon and others. The copolymer (like celcon) is somewhat
softer and weaker than the homopolymer making it easier to cut (even though you hardly notice the difference when the knife is very
sharp); but plectra cut from it also do not last as long. Even among homopolymers from different sources longevity varies. We use
the homopolymer Delrin® for plectra because of its superior durability. We offer natural (whitish) Delrin®, black Delrin® and black
Celcon®, both carbon filled. However, there is a problem with natural Delrin® as it comes from the mill, because it tends to be brittle
and the plectra cut from it may suddenly snap. We therefore temper all our Delrin® plectra, strips and pieces in the same process
that reduces their thicknesses. For instance, to produce thick plectra (.021”) we start with .025” material. We selected material
and procedures which in our experience give long lasting plectra. If you have plectra from other sources, you can test a sample by
doubling up a plectrum upon itself: it should not snap.
There is a definite grain to Delrin® and Celcon®. Plectra have to be cut with
this grain running along the length of the plectra. Plectra cut in this fashion are very durable. However, when cut with the grain
perpendicular to its length, plectra break very rapidly. Other causes for early breakage can be traced to improper voicing where the
plectrum is nicked with the voicing knife or an uneven cut is made leaving ridges and valleys on the underside.
Delrin® and Celcon® in
sheet form for plectra come from the mill in nominal thicknesses of .015”, .020” and .025”. Actual thicknesses may vary from this
by as much as 0.002”. Delrin® and Celcon® can be rolled out to lesser thicknesses by a careful technique that preserves the temper.
Doing so will actually improve its characteristics as a plectrum material. Thus we can offer Delrin® and Celcon® plectra in various
thicknesses and hold the thickness to closer tolerance.
The outer layer of Delrin® and Celcon® plectra is slightly harder than the
interior. Thus when the plectra are thinned with a scalpel during the voicing process, usually on the underside, this harder skin
is removed, which will cause the plectra to curl up slightly in time. As this happens the instrument may have to be re-regulated.
This phenomenon may be welcome if slots for plectra in the jacks are perpendicular to its surface. However, if the slots are at a
5 degree angle as is the practice for birds’ quill, it can be a nuisance. To avoid these problems and to simplify voicing, we recommend
selecting plectra of the proper thickness so that fine voicing can be limited to cutting away at the width only. When replacing a
few plectra, stay with the material already used in the instrument. The following comments may help you decide if you intend to re-quill
the whole instrument or build a new instrument.
DELRIN® is a registered trademark of E.I du Pont de Nemours and Company.
Natural Delrin® gives the longest lasting plectra if they are not brittle (see the discussion above). If properly annealed, cut and
voiced they seem to be indestructible. We know of professionally played instruments, where the bulk of the plectra have lasted more
than two decades. Plectra are very snappy and somewhat harder to voice. They work harden in time so that the voicing may have to be
gone over after they have been played in for a while.
Black Delrin® comes in at a close second as to longevity. They do not seem to
suffer from the delayed work hardening of natural delrin plectra, nor is brittleness of the material as big a problem. They cut a
little easier than natural delrin, even though this is not an issue if the proper thicknesses are selected.
Black Celcon has been proclaimed
by some as the ultimate plectrum material. However, the claims made for it have not held up by objective testing. Its tensile and
shear strengths are lower than those of Delrin®, which explains why plectra tend to break more rapidly. In listening tests, musicians
could not reliably tell the difference between natural Delrin®, black Delrin®, and celcon, but they could tell the difference between
these and birds’ quill. However, celcon does cut easier and thus is somewhat easier to voice when the thickness has to be reduced.
Also, the player may well feel and hear the difference which a keen listener cannot.
Birds' Quill is the traditional material for plectra.
It is not long lasting, difficult to voice, but it gives a unique feel to the touch of the instrument, which is hard to match with
the above man made materials. Historically, feathers from goose,crow, raven, and various birds of prey have been used.