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The Instrument Workshop
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Parts, plans and supplies for early keyboard instruments and other non-bowed stringed instruments
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Properties of Plectra Material
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Phone: 541-552-0989 Toll free: 1-800-442-6038 (US only) Lutz Cell Phone: 541-210-2701 Fax: 541-488-5846
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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.
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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.
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