Noisy Lead - Lead Composition

In my earlier posting “Wooden Week” I mentioned how loud woodcase pencils were. I received some feedback on this statement that has prompted me to do a little thinking. So just when you thought it was safe, that pencil geek nerdiness could go no further……….

Now I’m no acoustics expert, and I haven’t gone out and hired an expensive sound level meter, oscilloscope and other equipment to conduct this investigation. I am instead relying on my two head mounted listening flaps.

My comment that woodcase leads were noisy was based on writing with the HB grade pencils of Wooden Week in comparison to a couple of mechanical pencils. To my ears there is just no contest, woodcase pencil leads are really noisy, but noise and loudness, good or bad, are subjective things. As Woodchuck commented, “Of course the sound of the pencil is also part of it's charm”. But then there is also a saying about one mans quiet mellow easy listening music being my neighbours deafening punk rock nightmare. So is there any logical reason why mechanical pencil lead should sound different to, and possibly be quieter than woodcase pencil lead? I think the answer is yes.

Mechanical and woodcase pencil leads are not quite the same substance, as they are made from different raw materials. Manufacturers regard the finer details of their lead compositions as trade secrets so this is just general basic level information. Normal pencil lead is a “ceramic” lead - primarily a mixture of graphite, clay and grease/wax. The graphite marks the paper and the clay is the binder that holds the mixture together. This composition does not have the strength to withstand the demands of thin lead mechanical pencils in the typical 0.3 to 0.9mm diameter range. These thin mechanical pencil leads are “polymer” leads - the mixture is graphite (and possibly carbon black) to mark the paper, and a polymer replaces the clay as the binding agent and oil sometimes replaces the grease/wax.

Graphite and Carbon Black are both basically different forms of the same thing, i.e. carbon. “Carbon Black” seems to be used to distinguish very fine carbon black particles from larger “Graphite” particles. I don’t know exactly what type of polymer is used as the binder. Whenever I see “polymer” I immediately think “plastic”, which is what some manufacturers imply with wording like “synthetic resin” or “carbon skeleton”, but one manufacturer is a little more specific, using the wording “high polymer on the base of a natural material” and then talking about carbon fibre strands from a cellulose (plant matter) base. Of course many plastics are made from “natural” materials, like the celluloids (from plant matter) and casein (from milk) as opposed to “unnatural” materials like petrochemicals. I often look at the buttons on an expensive suit and consider how they started out as cows milk. Anyway it doesn’t really matter what the polymer is – the point is that the binder is not clay.

Since woodcase and mechanical pencil leads are not the same substance, it’s obviously possible that they sound different. I could also imagine other factors like the size of the graphite and the clay particles, and their proportions in the mixture having an impact on the sound of the lead. Soft grades like 6B and 4B would sound different to hard grades like 4H. I tested some Staedtler Mars Lumographs in these grades and could hear a big difference. On some smooth papers the 6B & 4B woodcase pencils were silent while the 4H was still quite “scratchy” sounding.

There are also other possible reasons for noise difference. Only a very short length of a mechanical pencil lead is held by the pencil mechanism, and the rest of the lead is enclosed within, but not attached to, the mechanical pencil body. So it’s inside a (possibly) sound insulating container. This arrangement could also limit the pencil body resonating the noise of the lead. On the other hand, woodcase leads are specially bonded to the wood along their entire length so the whole pencil could vibrate and radiate the sound. This would also imply a possible sound change as the pencil was sharpened and got shorter. Also of course how hard you push the lead into the paper could have a volume effect. And then there’s possible volume effects from the type and coarseness of the paper, the desk underneath…..

This is all getting a bit complicated, I’m sure there is a Masters or PhD thesis in all of this! Alatavista and other search engines bring up some serious research involving breaking pencils and leads. It seems ill-treating pencils in the name of science is ethically acceptable. If you are crazy you can check out this foray into the diamagnetic properties of mechanical pencil leads! It actually raises even more questions about quality control and noise variations.

I would like to thank “Steve” and an anonymous correspondent for their thoughts and suggestions on this subject. I think I need to seriously consider the state of my mental health, so I’m off now to watch rugby, gnaw on tough charred half-raw BBQ steak and drink beer - got to try and get rid of that pencil nerd!