Klarinet Archive - Posting 000304.txt from 2004/09

From: "Lelia Loban" <lelialoban@-----.net>
Subj: [kl] Cracking a glass vase with high notes?
Date: Sat, 18 Sep 2004 14:23:28 -0400


About a week ago, Karin Berman wrote,
>Have any of you ever had the case where,
>immediately after playing some high notes,
>a vase, or glass breaks? My beautiful thick
>blue glass vase (about 6 years old and in the
>shape of an old-fashioned vase), cracked as
>I was coming down the stairs to answer the
>phone. (Interrupted practice). The phone
>was near the vase, where it stood on a table.
>A loud crack erupted, giving me a big fright
>and left a neat hole about 1" in diameter and
>then cracks appeared and spread all over the
>vase, with the water pouring out.
[snip]
>Can anyone give me an idea if this was indeed
>related to my screech stick?

danyel wrote,
>I understand the issue is not so much the
>amplitude but the frequency of sound; if it
>matches the resonance of an object that vibrates
>easily, the idea would be to make it vibrate
>sympathetically so heavily that it breaks
>itself.

I'm a retired stained glass artist, catching up on the list and coming to
this thread late because, coincidentally, I've been moving my old stained
glass studio out of the basement and into the new shed. (My husband and I
finally have separate work benches!) Though I've never seen anyone shatter
glass with a clarinet tone, it's true that sound waves can break glass, if
the note is the right frequency to set up sympathetic vibration in the
glass.

Tim Roberts wrote,
>>I would guess it more likely that temperature fluctuations
>>and physical vibrations from the phone aggravated a
>>manufacturing flaw in the vase.

You're both right. Sudden, extreme temperature change or a sympathetic
vibration from a sound or other source can break glass, but breakage is
much more likely in glass that's weak because of the manufacturing defect
of poor annealing. There's no one specific amplitude or frequency of sound
or vibration that shatters glass. The breaking point depends on the
thickness and composition of the glass and on the amount of stress trapped
in the glass.

The glass vase was formed at a high temperature, either by blowing melted
glass on a blowpipe or by melting glass frit (ground glass) in a mold in a
kiln. Annealing means tempering the glass by cooling it very slowly in a
kiln, often a separate kiln set up as the annealing oven. Manufacturers
try to save money on fuel for large, industrial kilns, by keeping the
annealing time to a minimum. Bad annealing means that the manufacturer
cools the glass too fast, trapping stress in it and leaving it brittle.
Karin Berman's excellent description of the *way* the glass broke, with a
sudden "hole pop" followed by the appearance of many cracks spreading out,
gives a classic example of one type of annealing failure.

It's possible that either the phone or a clarinet note caused fine cracks
to form in her vase. Glass is a frozen liquid: Think of rotten ice
bending when you step on it. The hole popped out at the point of maximum
distortion and that shock caused the rest of the glass to go ahead and
release its stress. What she saw was the sudden widening of stress cracks
that were already there, but too fine to see until the physical vibrations
from her footfalls down the stairs -- or from the phone, or both --
finished the job by "running the cracks," which means breaking the cracks
open, the way a tap from the ball end of a glass-cutter breaks open the
glass along the score-mark from the cutting wheel. The other typical
pattern is crazing, where a fine network of tiny cracks suddenly spreads, a
phenomenon my friends and I used to produce deliberately when we were
children, by boiling glass marbles in water on the stove and then dropping
the hot marbles into a metal bowl full of ice water. Glass may craze just
before violently exploding, or it may stay together for years before
something jars it enough to crumble it apart, or anything in between can
happen. In Mexico, I've seen crazed marbles used as decorative "jewels" in
pottery lamps.

To stage the classic scene of the soprano's high note shattering a wine
goblet (assuming it's not a totally fake demonstration), the props manager
prepares several wine glasses (or as many as needed for experiments plus x
number of concerts) first, by having all of the glasses heated in a kiln to
about 950 degrees F., into the annealing zone but not hot enough for the
shape to distort. Then the glass is cooled down quickly enough to
guarantee that it loses its temper, but not so quickly that it simply
explodes in the kiln. (When we talk about a person "losing his temper,"
it's a metaphor.) The soprano then experiments by testing one goblet at a
time (with the other goblets safe where they can't hear her) until she
knows for sure which note will shatter this particular type of glass. Then
she and her accompanist(s) find or transpose a song to make that note the
high, sustained climax of a phrase. That's where we get the idea that it
takes a loud, high note to shatter glass: In reality, it may be nowhere
near the singer's highest note, but singing it as the climax of a phrase
makes the demonstration more dramatic!

Anyone who experiments with using a clarinet tone to shatter glass should
be aware that if the glass explodes instead of simply breaking, sharp
shards may fly in all directions.

Lelia Loban
America can do better: Kerry and Edwards in 2004!

------------------------------

Date: Sat, 18 Sep 2004 13:59:02 -0230
To: <klarinet@-----.org>
From: "Shadow Cat" <shadowcat666@-----.net>
Subject: [kl] Cracking a glass vase with high notes?
Message-ID: <13downwithrodents666>

I'm making my stupid pet human type this. She wrote,
>Though I've never seen anyone shatter glass with
>a clarinet, it's true that sound waves can break glass,
>if the note is the right frequency to set up sympathetic
>vibration in that particular piece of glass.

Your horrible screech-sticks can break a cat's ears, too. I've just
recovered from what the veterinarian (upon whom I wish a plague of
fleas--she's probably an outer space alien in league with supernatural
corruption) ignorantly diagnosed as an ear infection, but I know the
screech- sticks caused it. Deliberately. Maliciously. It was an act of
screech-stick terrorism, that's what it was. At least Lelia stopped
playing while I was ill, but now she's starting it up again and it's all
the fault of you people!

SSSSSSSsssssst!
Shadow Cat

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