Rob Parsons raised the issue of sacs, a more complicated business than it might at first appear. For years we were offered sacs that we were told were silicone but were actually PVC. Now the real thing is on offer. They are good sacs. Some people imagine that they are “better” in some way than latex sacs. This is not true. They have a purpose and their use should be limited to that. They are useful for celluloid patterns that are likely to be spoiled by a failing latex sac: jade, black and pearl, lapis lazuli and some others. The downside is that they provide more resistance to the mechanism than latex sacs and may apply too much pressure on levers and pressure bars.
Pliglass sacs look somewhat similar but are very different. They are used only in Parker Aerometric fillers such as the British Duofold and later Parker 51s. They have the wonderful property that few fail and and they are likely to last until the human race is no more. The few that do fail are the result of damage. They discolour but this is not a reason for replacement. Proper Pliglass replacements are available now.
Finally we get to latex sacs, by far the best solution for hard rubber pens or celluloid ones that will not discolour. They are very flexible and are therefore less demanding on filling mechanisms. They do fail through time and indeed it might be said that they begin failing the moment they are made. However this is a slow and imperceptible process. Latex sacs last a long time. As I said earlier I would expect this not to be a concern for eight to ten years. Many last much longer and I have heard stories of vintage pens being opened and found to contain a perfectly pliable original sac!
A concern was mentioned that the price of latex sacs is rising. The Pen Sac Company (the only manufacturer of latex sacs now) finally applied a modest increase in the cost of latex sacs few months ago. The price had remained at the same level for years and years. Because I use a lot of sacs I buy from the source and I don’t know what price rises have been applied by retailers. To be fair to them, they have to cover the import costs, as I do, and they are quite steep. I would say that they are only justified in raising their prices once in recent years, given that The Pen Sac Company only raised theirs once. How retailers charge for sacs is their business. Shop around.
I love latex sacs. They are much less bother than the alternative. Shellac fixes them firmly and never fails whereas you have to hunt around for adhesives for the other kinds and they are not always as reliable and easy to work with.
Finally, I regard The Pen Sac Company as the vintage pen hobby’s saint. The owners have restored old, failed machinery and made the production of all shapes and sizes of sacs possible. Without their determination to make restoration of old pens possible we would only have those vintage pens under glass, to be admired, not used. Way back when I started out in this hobby I didn’t know where to get ink sacs. There was no Internet to guide me and I had a splendid early Waterman with a wonderful nib. I could only use it as a dip pen. Thank you, The Pen Sac Company.