The making of hard rubber

Some pen videos · June 23, 2006

If you are interested in some interesting visuals on the making of hard rubber

follow this link http://www.clarinetmouthpiece.com/story_rubber.asp (scroll down for the pictures).

It is not about pens but about reproduction vintage hard rubber clarinet mouthpieces. The concept is the same.

The pictures in the link above show very nicely the procedure of mixing the natural rubber latex with sulphur, which is the key to vulcanization

(what changes the liquid rubber latex into solid rubber), and other "secret" ingredients. The "key" step in rubber production is the incorporation of sulphur and other ingedients before rubber becomes solid.

The image below is a schematic (approximate) representation of the molecular structure of rubber, where the surphur atoms (yellow) crosslink the long chains of the polyisoprene (natural rubber). More surphur "bridges" make the rubber harder. The hard rubber of pens (ebonite, or vulcanite) is a heavily crosslinked rubber.

http://www.clarinetmouthpiece.com/img_story/10sulfurrubber.jpg

http://www.clarinetmouthpiece.com/img_stor...ulfurrubber.jpg

Other than sulphur, the most common ingredient is carbon black (essentially the powder that is in the printer toners - very fine powder with diameter about

100-1000 times smaller than the diameter of a human hair). For those that are into the technical jargon, rubber with carbon black

is indeed a "prehistoric" nanocomposite.

The addition of carbon black in the form of lampblack (fine shoot from icompletely burned materials) to rubber is attributed to T. Hancock of UK

in the late 1830s (before Charles Goodyear in the US). So the Black in Black Hard Rubber (BHR) is carbon.

The "red" in red hard rubber (RHR) was discussed in this FPN post by George Kovalenko some time ago.

Many other additives are included in rubber. In the early work magnesia, lime, oxides and salts of lead were used to give color, help processing

and improve properties of rubber. Modern rubber is even more complex. In addition to sulphur and carbon black, other rubber additives include:

stearic acid, pine tar, zinc oxide, calcium carbonate and many other propriatary compounds. These materials play various roles: some accelerate the vulcanization,

other act as antioxidants and antiozonants. Antioxidants and antiozonants are keys in retarding the oxidation of rubber. This is a subject that I hope to comment on in the following weeks.

Edited June 23, 2006 by antoniosz

June 23, 2006

Thanks for the info.

June 23, 2006

all i need now is some rubber trees, sulfur and one of those internal pressure machines

June 23, 2006

Antonios--

Very interesting! If you are still researching this, as the close of your post implies, I hope you will think about submitting this to the PENnant, as it would make a very interesting piece.

best, Dan

June 23, 2006

antoniosz: Your post mentioned salts of lead, which does indeed get a big thumbs down. What do you think that the likelyhood of running into HR fountain pens with lead salts in them is? I have had my eye on a couple, but...

Some pen videos · June 24, 2006

antoniosz: Your post mentioned salts of lead, which does indeed get a big thumbs down. What do you think that the likelyhood of running into HR fountain pens with lead salts in them is? I have had my eye on a couple, but...

You are bringing up a VERY IMPORTANT point.

I hope I do not sound too alarmist here, but the original patent for rubber No 8075 by Nelson Goodyear clearly states that "Rosin, oxides or salt of lead or zinc of all colors and other similar substances both mineral and vegitable can be added in small quantities ... for the purpose of polish, color, making the mixture work more easily etc.". Given that concern for lead came up much later, I would no be surprised that there is lead in HR ... I am going to follow this up.

PS> It could be that this explains the behavior of some pen hobby elders :ltcapd:

Edited June 24, 2006 by antoniosz

June 24, 2006

antoniosz: Your post mentioned salts of lead, which does indeed get a big thumbs down. What do you think that the likelyhood of running into HR fountain pens with lead salts in them is? I have had my eye on a couple, but...

Well, as long as you don't intend to feed it to your children..........

Some pen videos · June 24, 2006

OK. Here is one interesting piece of information. National Geographic October 1923

A promotion campaign for lead Look at the top middle item... A BHR pen.

Definitely worth following up more.

http://mywebpages.comcast.net/azavalia/NG-Oct-1923.jpg

PS> The tragic irony of this ad campaign for lead is that "in 1921 the president of the National Lead Company, Edward J. Cornish, wrote to David Edsall, the dean of Harvard Medical School, saying that lead manufacturers, as a result of "fifty to sixty years" experience, agreed that "lead is a poison when it enters the stomach of man--whether it comes directly from the ores and mines and smelting works" or from the ordinary forms of carbonate of lead, lead oxides, and sulfate and sulfide of lead." (http://www.cincinnatichildrens.org/researc...l-knowledge.htm). Amazing.... (see http://www.cincinnatichildrens.org/researc...ead-advertising for more historical info).

Edited June 26, 2006 by antoniosz

June 24, 2006

OK. Here is one interesting piece of information. National Geographic October 1923
A promotion campaign for lead Look at the top middle item... A BHR pen.
Definitely worth following up more.

http://mywebpages.comcast.net/azavalia/NG-Oct-1923.jpg

Well, as long as you don't intend to feed it to your children..........

Ack! That's terrible!

And in regards to not feeding it to your children, I believe it's generally a good idea to avoid using things with lead which could leach easily from them, regardless of intent to consume or not.

Shocking that there was an entire campaign for it. Certainly, industry has come a ways, and could definately come a way more.

R.ticle One

Edited June 24, 2006 by R.ticle One

Some pen videos · June 25, 2006

R.ticle One,

I dont want to sound (too much) alarmist. I am not sure if there is a danger at all.

Actually hard rubber stems are often found in smoking pipes and some clarinet mouthpieces. My guess is that modern hard rubber is not a problem.

Vintage? I simply dont know. At this point it would be best to hear from someone who is an expert.

PS> The good thing is that rubber tastes awful, so biting into it is less likely than the other plastics

Edited June 25, 2006 by antoniosz

Some pen videos · June 26, 2006

Some background information. From http://www.epa.gov/ttn/atw/hlthef/lead.html

"Exposure to lead during pregnancy produces toxic effects on the human fetus, including increased risk of preterm delivery, low birthweight, and impaired mental development. These effects have been noted at maternal blood lead levels of 10 to 15 µg/dL, and possibly lower. Decreased IQ scores have been noted in children at blood lead levels of approximately 10 to 50 µg/dL."

Soem back of the envelope calculation:

10 micrograms per deciliter is the detectable effect limit.

The human person has about 5 liters of blood (http://hypertextbook.com/facts/1998/LanNaLee.shtml). This means that detectable effect limit is a whooping 0.5 milligrams of lead in the blood system.

A typical BHR pen is about 10 grams. If a 0.1% of it is lead (typical additive level) then it contains 10 milligrams of lead. Of course it is inside the rubber, and the amount that one might get from biting or chewing is small but it still feels uncomfortable for me. Presumably hard rubber machining is also something that needs to be done with some care.

So I am not ready to completely dismiss this before we hear from someone that knows more. In the mean time, I think common sense suffices. I am not dumping my HR pens anyway

Edited June 26, 2006 by antoniosz

June 26, 2006

Still not chewing my pens nor letting the little ones do so either. My grade school principal would be calling this making a mountain out of a molehill. A real risk is putting scotch into a lead crystal glass because it does leach out lead that you actually would drink.

Roger W.