It would depend on what density the welders glass is, if it's a low grade it wouldn't be all that safe I'd imagine.
NASA suggests that number 14 welders glass would be acceptable but at the same time unless it has been specifically designed for solar viewing then it cannot be regarded as %100 safe.
http://eclipse.gsfc.nasa.gov/SEhelp/safety.html
You could always try these if stuck for a safe option.
http://www.iceinspace.com.au/forum/s...ad.php?t=90481