This could also have been called optic destroying with collodion. You’ll see why in a bit.
Based on my first three attempts, I wouldn’t recommend bothering to use collodion with cheap mirrors.
Collodion is used for a number of applications, such as cleaning optics used in astronomy. It was recently mentioned on the Holography forum as a way to clean our precious mirrors and lenses.
Here’s the first mirror with a tape dam at an angle which attempts to show all the crud on the mirror. It’s not excessively dirty like you might get with optics used in astronomy but it’s dirty enough that it’s interfering with my reference beam light. The mirror is used to steer the light coming out of my spatial filter up to my collimating mirror and needs to be as clean as possible. Note that this was a cheap $1 mirror I bought at a local electronics shop.
This is the same mirror after the collodion has been applied. I had to wait about 10 minutes for it to dry completely since the layer was somewhat thick.
Pulling away the tape helped to release the dried collodion layer but also showed that the silver was coming up too.
I performed the same process on a more expensive Edmunds mirror and had no problems. Sorry, no pictures.
The collodion wasn’t always easy to remove, sometimes a bit would remain behind. In those cases I dripped a bit more collodion on the offending spot so that I ended up with a thicker dried area afterwards and was able to remove the final spot with my fingernail or in one case a piece of tape.
Here’s the same process being performed on a cylinder lens I also use in my reference beam.
After applying the collodion
Removing the collodion