Prism re-silvering with silver nitrate? Anyone done it?

[paradoxbox]

I am planning to resilver and CLA an M3 that has a blacked out finder myself. The M3 was apparently dropped 20 years ago and so the original silvering is likely totally corroded.

I'm going to do the resilvering job with a silver-nitrate solution as was used in the mirror making industry and for telescopes for ages - but I have heard that the color cast is different from the usual aluminum silvered beam splitters.

Has anyone ever used an M3 or any kind of camera that was half-silvered with actual silver nitrate, and what did you think of it?

 

[maddoc]

I would think that you want a semitransparent mirror to see both, VF and RF image. Your silver-nitrate method will most probably generate an opaque 100% reflecting mirror, so you would only see the RF patch. Alternatively you could experiment until you get an evenly distributed semi-transparent mirror over the complete surface, no easy task though ... 😉 (I have coated literally hundreds of Pt, Au, Cu, Ag, Pd layers onto Si and glass surfaces at laboratory)

 

[paradoxbox]

well the chemicals i intend to use produce a slower reaction than the normal method that is posted on youtube, both methods will produce a 100% coating if allowed to do so. but i intend to stop the coating once the mirror reaches around 70% transmission. i've done some practicing on glass with this and have the process down close enough to provide useable results, but i'm curious about how it will actually look when i do it to the prism itself.

i've heard that there may be a slight pink cast and that the image itself will be much brighter and clearer than the original aluminized prism.

 

[astro8]

Interesting stuff. Let us know how it works out.

 

[sevo]

I would think that you want a semitransparent mirror to see both, VF and RF image. Your silver-nitrate method will most probably generate an opaque 100% reflecting mirror,

As I learned the hard way when re-doing front surface coated mirrors, it is actually quite hard to create a 100% opaque deposit. Still, reaching a well defined degree of semi-transparency will be even harder, at least if you only have one prism to experiment on...

 

[paradoxbox]

The nice thing about silver nitrate is that it can be completely removed in seconds with a little nitric acid and the prism re-surfaced immediately afterward. You have nearly unlimited attempts as long as the chemicals don't wear out.

I'm planning to make a test strip of glass with 10% gradations from completely opaque to completely transparent and will try to match the prism's mirroring to the 30% level of the test strip. Once that's done I'll immediately UV glue it to the other prism to prevent tarnishing.

 

[mooge]

funny seeing this... I thought of doing the same sort of thing about a week ago.

What's the plan? Rochelle salt method? and why 70% transmission? (how do you test % transmission anyways?)


and do let us know how it goes... my silver nitrate is in the mail...

 

[paradoxbox]

70% transmission was from a figure I found somewhere on here or another photography website where somebody listed the various transmission ratios of leica beamsplitters. I'll have to find it again but I'm pretty sure the M's are 70/30.

About testing transmission, the only way you can do it is with something like a densitometer, or if you don't care about hitting an EXACT percentage then you can just make a rear silvered test strip at 10% gradients like I am going to do and clearcoat it afterward so it doesn't tarnish.

I'm planning to use the method proposed in this book:
http://www.jstor.org/discover/10.2307/1126309?uid=3738328&uid=2&uid=4&sid=21101985305807

 

[alfredian]

Beware the explosive side reaction

Beware the explosive side reaction

When handling silver nitrate be aware, and careful, of the side-reaction that can generate nitrate explosives. This was the classical hazard of the classical Ag/Silver Nitrate mirror-slivering process used in classical Newtonian telescope-making. It was the ultimate bad end to a very long, meticulous mirror-grinding process to have it shatter when the nitrates detonated.

Hence modern "silvering" is done with Aluminum vapor in a vacuum chamber. In my own experience I was an ear-witness to a student employee who reported to me a community college in Texas. His job one evening shift was to catalog & sort the lab cart full of spent/old chemicals & reagents destined for recycling/disposal. I was in my office down the corridor and around the corner and there as a very loud THUMP. One of the hal-liter brown bottles contained the leftovers from the chem departments faculty-demo of Mirror Silvering with Silver Nitrate. Fortunately my lad had bent over to pick up something he'd dropped on the floor. Other than buying him a new shirt, we got off easy. We were digging shards of brown glass out of cinder blocks, sheet rock and wood planks for several days.

The side reaction generates a "contact explosive" and once upon a time, in a happier, more innocent era, this was one of the thinks high school chem students would apply to the underside of toilet seats in the loo. Next time the seat was dropped, in a hurry...BANG.

Enjoy, carefully. Silver starts to tarnish & dim almost instantly, Aluminum Oxide is forever.

 

[mooge]

Any luck, paradoxbox?

My silver nitrate just arrived, all 5g of it. yaaay.

And the canada balsam samples are not really curing. oven it is...

 

[oftheherd]

When handling silver nitrate be aware, and careful, of the side-reaction that can generate nitrate explosives. This was the classical hazard of the classical Ag/Silver Nitrate mirror-slivering process used in classical Newtonian telescope-making. It was the ultimate bad end to a very long, meticulous mirror-grinding process to have it shatter when the nitrates detonated.

Hence modern "silvering" is done with Aluminum vapor in a vacuum chamber. In my own experience I was an ear-witness to a student employee who reported to me a community college in Texas. His job one evening shift was to catalog & sort the lab cart full of spent/old chemicals & reagents destined for recycling/disposal. I was in my office down the corridor and around the corner and there as a very loud THUMP. One of the hal-liter brown bottles contained the leftovers from the chem departments faculty-demo of Mirror Silvering with Silver Nitrate. Fortunately my lad had bent over to pick up something he'd dropped on the floor. Other than buying him a new shirt, we got off easy. We were digging shards of brown glass out of cinder blocks, sheet rock and wood planks for several days.

The side reaction generates a "contact explosive" and once upon a time, in a happier, more innocent era, this was one of the thinks high school chem students would apply to the underside of toilet seats in the loo. Next time the seat was dropped, in a hurry...BANG.

Enjoy, carefully. Silver starts to tarnish & dim almost instantly, Aluminum Oxide is forever.

Who knew? Thanks for the info.

I hope that isn't the reason paradoxbox hasn't replied. 😛

 

[icebear]

Any luck, paradoxbox?

My silver nitrate just arrived, all 5g of it. yaaay.

And the canada balsam samples are not really curing. oven it is...

I had a M3 CLA'd by Don (DAG camera) and he had to re-glue the prisms but the silver was still ok. I think, the Canada balsam is the culprit over time. If historical accuracy is the goal here then this material need to be used again but a more modern glue should avoid the same problems. I'm not sure though what Don is using to glue the prisms together.

 

[paradoxbox]

i haven't had time to do this yet, too busy with work stuff.

about synthesizing silver fulminate, i think that it's a pretty long shot as that requires certain specific conditions and a number of big mistakes need to be made before it will become explosive. by itself silver can be left in a jar of nitric acid and it will just turn itself into silver nitrate with the remaining acid evaporating off after a while.

i am still nervous about the fumes though and am investigating what to do about that.

 

[KoNickon]

This is a fun thread -- you are way more adventurous (and knowledgeable) than I would ever be. Looking forward to hearing how things turn out.