If the SolarViewers are handled with care, they will last for a long time – most probably much longer than we can state publicly. Official certificates are not valid for infinity – otherwise, we would have to commission very expensive long-term tests – and nobody can give us a warranty for having stored his viewer properly. This is the reason why we can’t advertize on our website that you can use the film for decades if you handle it with care. This is somehow the same problem as with canned food: A carefully sterilised can of food will last for up to 50 years without even changing its taste – but nobody will (may) write this on a can…
At least, we ourselves still store some SolarViewers from 1999 here which we still use for a quick look at the sun to see what’s going on there. We were surprised and happy to see how many people called us in the last days before the last german-eclipse in March 2015 and wanted to know if they can still use their SolarViewers they kept from back in 1999. That was 16 years ago and shows us, how much people valued the memory of that event.
Our answer (in March 2015) was always the same:
If there are no obvious scratches or damages showing up when holding the viewer towards the sun and if the sun does not appear to be inconveniently bright, then the film most probably is still fine and you can use it – but unfortunately we cannot take over a warranty. Please note that the newest standards say that you are to take a break after every three minutes of observation. We concur with that.
UPDATE: Since the DIN Norm changed in 2015 and our old viewers don’t reach the latest norm anymore, we can’t legally recommend to use them anymore. We advise everyone to purchase our ISO 12312-2:2015 compliant Solar Viewer AstroSolar Silver/Gold. Those are certified as safe and can be stored indefinitely according to the DIN norm which is quoted on the official AAS website (see quote below):
Quote by Rick Fienberg, AAS Press Officer:
Some eclipse glasses and solar viewers, even new ones, are printed with warnings stating that you shouldn’t look through them for more than 3 minutes at a time and that you should discard them if they are more than 3 years old. Such warnings are outdated and do not apply to eclipse viewers compliant with the ISO 12312-2 international safety standard, which was adopted in 2015. If your eclipse glasses or viewers are relatively new and are ISO 12312-2 compliant, you may look at the uneclipsed or partially eclipsed Sun through them for as long as you wish. Furthermore, if the filters aren’t scratched, punctured, or torn, you may reuse them indefinitely.