For over a century talc has been used as a standard dry lubricant for rubber fountain pen sacs. The slippery mineral dust helps to protect the sac from friction damage when it is depressed by a pressure bar. This lubrication is also essential for Parker Vacumatics and other pens where a sac is folded in on itself; rubber sticks to itself, and the mechanisms of these pens simply do not work without lubrication.
In recent years there has been a great deal of attention given to the possibility of asbestos content in talc products. Asbestos is often found in the same deposits as talc (http://dx.doi.org/10.18103/mra.v8i5.2097), and has been proven to be a carcinogen (cancer-causing). While there are cosmetic-grade talcs, it is recommended that any talc without reputable certification as asbestos-free be assumed hazardous (Asbestos in Talc Powders and Soapstone – the Present State ).
I like my lungs. And suddenly the little puff of white coming out of a lever slit after you have replaced a sac feels ominous, instead of satisfying. None of the talc suppliers I have contacted seem able to provide information about sources, or safety. So, following the excellent advice of the German government (see link above), Restorers Art is immediately discontinuing the use of talc as a sac lubricant.
An Excellent Alternative
All this being said, there is good news! There is an excellent alternative dry sac lubricant.
The personal care industry turned to the use of vegetable starches, like corn starch, as an alternative to talc. We investigated that as an option. We found the particle size too large, and starches turn gummy if wet, which is a terrible quality for our application (think pen leak here: eeeew!)
We have, however, found an excellent alternative: precipitated calcium carbonate (CaCO3). This is a powdered chalk produced from limestone, and has been used for centuries in bookbinding and shoemaking. Particle size ranges from 0.2-30 μm (compared to talc at 0.2-100 μm). The “precipitated” description means that the chalk has been purified and contains nothing but CaCO3.
We have done our own experimenting (the best kind!) and created a slurry of CaCO3 in filtered water. We let the water evaporate, then tested the newly dried CaCO3. The wetting-drying cycle did not seem to affect the lubricating quality of the lubricant in any way. Which for us is a big win! It does not dissolve in water, but rather forms a suspension.
This slurry has a pH of about 9.0, which is alkaline. This is actually good for us, because the interior of a pen is damaged far less by alkaline conditions than acidic. (As an example, steel pressure bars, buttons, springs, or nibs will rust very quickly in acid fumes, and even corrode right away when bathed in acid. Alkali won’t affect these materials this way.)
Another advantage is that CaCO3 is inexpensive, and fairly easily available. And a 100 gram bag will be enough to last for years of new sacs.
While the chances of contracting cancer from a bit of talc in a fountain pen may be minimal, we like to play it safe. CaCO3 is a cheap, effective, and available alternative. So why not choose safe? After all, with all the nasty chemicals out there, there is nothing wrong with making sure the pens we carry with us, and use every day, are the safest things around!