Welding mask for the eclipse: only with a shade 12 filter or higher, and never auto-darkening

Yes, but only if the filter is shade 12 or higher: that’s the minimum the American Astronomical Society (AAS) and NASA give for looking at the Sun with the naked eye. The AAS puts the sweet spot at 13 or 14 and asks people not to use adjustable or auto-darkening helmets. If you don’t know your filter’s number, don’t use it. And you’ll need it all morning: in Tarifa, the Moon starts covering the Sun at 09:40:56 and doesn’t let go of it completely until 12:00:35 (Spanish time, CEST, UTC+2). The only spell without a filter is totality, and the exact second it starts and ends is in when to take off your glasses.

What number you need, according to whom

In a welding mask, what protects you is the filter, and its darkness is expressed as a number: the protection level, also called the “shade”. The higher the number, the darker the filter:

The safety page that NASA published for the 2017 eclipse says almost the same: the only welding filters that are safe for looking at the Sun with your eyes are those of “Shade 12 or higher”. It adds that many people find the Sun too bright even with a 12, and others find it too dim with a 14, and that 13s “are uncommon and can be hard to find”. B. Ralph Chou’s eye-safety text on NASA’s eclipse website lists “shade number 14 welder’s glass” among the safe filters that are easiest to get hold of.

How to read your mask’s number

In Europe, welding filters are covered by two standards, according to the data sheet on welding protectors from the INSST (Spain’s National Institute for Safety and Health at Work). UNE-EN 169, “Filters for welding and related techniques”, covers fixed-shade filters. UNE-EN 379, “Automatic welding filters”, covers those that change shade by themselves. The same sheet explains that the protection class (a code and the shade number) is marked only on the filters, and that in welding the shades range from 1.2 to 16.

To check yours:

1. Look for the number on the filter itself, not on the shell or the box.
2. If it’s lower than 12, if you can’t find it or if you can’t read it, that mask is no good for the eclipse. NASA sets it as a precondition: “make sure you know the filter’s shade number”.
3. If your mask is the kind that darkens by itself, the UNE-EN 379 kind, read on: it won’t do even if it shows a high number.
4. If the glass is scratched, cracked or loose in the frame, throw it out. That’s the AAS rule for any solar filter: “if scratched, punctured, torn, or otherwise damaged, discard it”.

Why hardly any mask at home makes the grade

NASA takes it for granted in that “and it probably is”: if you have an old mask lying around at home, its filter is most likely below 12. And the AAS adds that shade 13 and 14 filters “are rarely stocked in welders’ supply stores”, so they’re easier to find online.

If you’re going to buy something for the eclipse, the logical thing is to buy something made for looking at the Sun: EN ISO 12312-2 glasses or a viewer. How to check them, step by step, is in our guide to certified glasses.

Not the automatic ones

The AAS puts it like this: “You should not use adjustable and/or auto-darkening welding helmets or similar products to view the Sun”. It gives two reasons: many of them don’t get as dark as a shade 13 or 14 filter, and even the ones that do pose a serious risk to your sight. Even if yours shows a high shade in its darkest setting, don’t use it.

If yours is dark enough: how to use it

• Like eclipse glasses. The AAS asks you to stand still and cover your eyes with the filter before looking up at the Sun, and to look away before taking it off, never while you’re looking.
• Naked eye only. No binoculars, camera or telescope behind the glass. Chou spells it out: with an optical instrument, don’t use any filter that isn’t made for that purpose and fitted on the front. That’s what solar filters for telescopes and binoculars are for.
• Off only during totality, and only inside the path. Outside the 105 towns with totality, the filter stays on all morning: the Sun is never completely covered.

If you don’t have one that’s dark enough

Sunglasses won’t do, however dark they are, and we explain why in sunglasses for the eclipse (in Spanish). With no filter at all you can still follow the eclipse by projecting the Sun, without looking at it, as we explain in the homemade viewer (in Spanish).

On Order your glasses you can ask for ours: cardboard, with the EN ISO 12312-2 certificate, along with the phone filter and packs for groups. We reply with the price and the delivery time.

Sources: AAS — How to View a Solar Eclipse Safely (shade 12 or higher; 13 or 14 as the sweet spot; 12 too bright and 15 too dark; shade 13 and 14 filters rare in welding shops; no adjustable or auto-darkening helmets; how to put the filter on and take it off; discard a damaged filter); NASA — Safety, Total Solar Eclipse 2017 (only shade 12 or higher; know the filter’s number; “less than 12 (and it probably is)”; 13 hard to find); B. Ralph Chou — Eye Safety During Solar Eclipses, on NASA’s eclipse website (shade 14 welder’s glass; no filter on an optical instrument unless it’s made for that and fitted on the front); INSST — Protectores oculares y faciales para soldadura (in Spanish: UNE-EN 169 and UNE-EN 379; the protection class is marked only on the filters; shades from 1.2 to 16); times for Tarifa: eclipseando data (skyfield engine + DE440s).