Tuesday, December 18, 2012

Silicone sacs are here at last!

Silicone pen sacs are the future, and we now have them! Latex ink sacs have been around for over a hundred years, but have recently begun to show their age. Many newer ink formulations have proven rubber-unfriendly, turning conventional sacs to goo in a matter of months or even weeks. And as latex rubber ages, it can give off sulfur compounds that will permanently stain celluloids and other permeable plastics.

Silicone, by comparison, is remarkably resistant to chemical action, and highly resistant to taking a set (most materials, if squeezed long enough, won't spring back all the way after a while; silicone will). It's also very stable, so not only will it last a long, long time, it will not break down and release anything nasty as it ages.

Which brings up another issue: what about those other companies' silicone ink sacs? A good question, in that we have not yet been able to find any. Shocking, yes -- but when we started testing various sacs that were being advertised and sold as silicone, not a single one turned out to be as advertised. While some may have had some silicone content, their predominant ingredient was PVC -- otherwise known as vinyl. PVC can be a very durable sac material, but it is a potential time bomb in celluloid pens. As it ages, PVC exudes a plasticizer known to attack celluloid, leaving deep scars wherever contact is made. Unfortunately, in the past several years many collectors and repairmen have installed these "silicone" sacs in their most valuable and best-preserved celluloid pens, inadvertently replacing traditional latex sacs with something potentially much more damaging.
This disheartening discovery was what spurred us to get into the pen sac business, manufacturing top-quality ink sacs guaranteed 100% silicone. As we also discovered, making vinyl sacs is easy, but real silicone is another story. Genuine silicone sacs have to be injection molded. You can see the telltale mold lines running the length of our sacs (click on the picture above to enlarge). The absence of such lines is a strong indication that the sac is either dip or blow-molded, and not silicone -- no matter what the seller claims.

At the moment we have silicone sacs in only one size, #18, but we will be expanding the range of offerings considerably in the coming year. Sacs are now available for purchase through our catalog and on eBay. We will also soon be posting a video showing how to test a suspect sac to see if it really is 100% silicone.

PS Note that there is a big difference between silicone vulcanized at high temperature (as used in medical-grade tubing, for example, and our sacs), and RTV (Room Temperature Vulcanizing) silicones, familiar as sealants and molding media. Some RTV silicones release acids as they cure, which can be a prolonged process. This is not the case with high-temperature vulcanized silicones.

PPS The video on silicone sac testing and identification can now be seen here.

PPPS A chart laying out the pros and cons of various pen sac materials is here.

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