rust colored by Deborah
Is the flux leaching into the mirrors in my stained glass pieces? If so, is there a kind that won’t discolor the mirror? Or is it the rinsing that does it? or cutting with oil on the cutter?
I have tried sealing the mirror pieces after they are cut – on both the backs and the sides – but something is still effecting it.
Would love some advice!
Hi Deb, thanks for your question and photos – it’s helpful for me to see what’s happening.
These spots are very common – sometimes a rust colour but most commonly black. It’s caused when the the reflective metal coating that backs mirrors becomes tarnished. Whenever mirror is cut, it creates a weak spot where contaminents – such as flux – can creep under the coating.
To give yourself a fighting chance, try to make sure you choose an acid-free flux acid-free flux.
But the secret is sealing the edges tightly with a mirror edge sealant. You can get this from most stained glass suppliers, eg Delphi
I have used a good quality nail varnish when I’ve run out of sealant.
It’s important to spray on both the back and front edges of mirror. Pay particular attention to the places where the backing is chipped, as this is where the corrosives do their nasty work!
I put my mirrors on a brick in a large shallow box, and spray around each edge, turning the box around.
Two coats is more effective than one if you can stand it. Do this before leading or copperfoiling.
I hope that helps for future projects.
How do I clean the sealant off the glass after it is sprayed all around. Will this harm the glass?
Mmm, it’s best to be very careful and not get the sealant on the front of the mirror as it’s hard to get off.
Try a a non-ammonia cleaner or Isopropyl Alcohol, but be careful at the edges as you don’t want to take it off the bit that’s protecting the back.
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