The Sac Debate

The discussion about sacs, silicone and otherwise, rumbles on. One unfortunate consequence is that some people are making a blanket condemnation of latex sacs. This is premature, at best. Those sacs that were sold as silicone previously, but are in reality a mixture of silicone and PVC, we are told, are much less flexible than latex sacs. Are the new, truly silicone versions stiff like them or fully flexible like latex? That’s not clear yet, or at least it isn’t clear to me.

Old pens were designed to be used with latex sacs. Some – Conway Stewarts and Watermans come to mind – do not well withstand the added stress of a stiff sac on aging levers and lever boxes. If we are left without a sac as flexible as latex as a consequence of this debate, I forecast great demand for Conway Stewart levers and Waterman lever boxes.

I think it needs to be said, too, that latex sacs are harmless and useful in all but a few pens. Some light-coloured pens like jade, lapis lazuli and some of the Waterman 1930s patterns like onyx do discolour badly due to the decay of latex sacs. However, if you have a celluloid or casein pen of almost any other pattern, it will be entirely unaffected.

Silicone sacs are not a universal panacea. The pattern of discolouring in many pens suggests that there is more than the sac at work. Other rubber components like inner caps and sections appear to add to the problem. It may be, of course, that after 60, 70, 80 years the material in these components has finished outgassing and they’re no longer harmful. But do we know that?

Finally, let’s not rush to too favourable a judgment on the new silicone sacs either. Surely we have learned now that in the pen world, it often takes years or decades before problems become evident. We are assured – and I have no reason to doubt it – that silicone is inert and therefore harmless. But is it adequately durable? Time will tell.

I caution against speedy decisions which we may repent at leisure, particularly with regard to the idea that we should dispense with latex sacs.


About goodwriterspens
I restore fountain pens, and used to trade as redripple52 in eBay. I also have my own fountain pen sales website,

3 Responses to The Sac Debate

  1. dc says:

    I see the whole bruhaha over silicone and PVC sacs as an argument in favour of using latex sacs. The only blanket condemnation coming from this is should be for PVC sacs – as I understand it, pens that can be safely used with PVC sacs can also be safely used with Latex sacs and pens prone to being damaged by latex are also prone to damage by PVC.

    • dc says:

      Actually, not even PVC should get a blanket condemnation, there are pens it can be used safely on, and in some of those it may be advantageous to use PVC. So long as manufacturers and retailers make it clear exactly what material their sacs are made from, there wouldn’t be a problem. Just options, some of which may damage some pens, but all of which have safe and appropriate uses.

    • If common sense prevails – and who can say whether or not it will – PVC sacs will disappear quite rapidly and the choice will be between the new silicone sacs and latex ones. For me, that’ will work out at a ratio of about 1 silicone sac to 10 latex ones, given the types of pens I restore.

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