Alright, then. It's decided. If I ever completely lose my mind and decide I need to make colloidal silver myself, it will be with a hand cranked centrifuge!
Originally Posted by Photo Engineer
Actually...you know...if I set things up right, when we lose power here in the winter for days at a time, I could still make emulsions. Bunsen burner, hand whisk, gaslight. Just kidding (I think).
THere's one of those on ebay right now.
Originally Posted by Photo Engineer
I don't think I'd like to try to make colloid using one of those centrifuges. That IEC is a tabletop clinical centrifuge with limited capacity and G-force. When you make a raw colloid solution--it's very dilute. My test batches were 2-4 liters, so that's a lot to try to spin down in a tabletop fuge. I can't recall the exact g-forces necessary, but you probably wouldn't be able to adequately concentrate the colloid with a small centrifuge. The colloid particles are pretty small (<100nm), so it takes some spin to pull them out of solution.
There are centrifugal UF and RO units for sale that spin out the mud but they are rather large and expensive. They use a spinning spiral path IIRC to collect the mud and express the water. Then you have to get the mud out.
I've silvered mirrors using the technique described in the back of every old CRC Handbook (of Chemistry and Physics, of course). I seem to remember that is gives the procedure for taking an ammoniacal solution of silver nitrate (really oxide) and then reacts it with Rochelle salt. This solution reduces the silver and as it drops from solution, it can coat any opbect placed in it's way - mirrors, the sides of the containers, anything in there. It's not a very abrasion resistant coating, and when thin it can easily be rubbed off. It's been over 30 years since I did this, but I seem to remember that it also created a lot of sludge. I suspect that was some collodial silver.
One of the links I gave above gave Rochelle salt (potasium sodium tartrate) as one of the reducing solutions, so I'm sure the chemistry will be similar to that process. I think rock sugar can be used as well, as can formaldehyde and many other chemicals.
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Originally Posted by Kirk Keyes
Last edited by Ray Rogers; 08-29-2008 at 05:31 AM. Click to view previous post history.
Colloidal silver can be almost any spectral colour. By varying the size and shape of a silver nanoparticle you can adjust the peak of it's reflectance right across the visible spectrum. It's a hot topic in current nanoscience.
First pic: a mixture of silver nanoparticles of various sizes and shapes as seen in an optical microscope in darkfield mode - you are seeing backscattered light here. (from Orendorff et al, Small 2, p636, 2006)
Second pic: Peak reflectances for various silver shapes and sizes. (from Mock et al, J. Chem.Phys. 116, p6755, 2002)
The second paper by Mock and Co. is the one to look for if you want a single reference. Otherwise a google search on "plasmon resonance nanoparticle" will turn up lots of relevant hits.
In the 50s Robert Bensley claimed to be able to tune the production of silver particles in photographic emulsions so as to produce full colour images. Current research makes it clear why this might work, but it is not at all clear that Bensley's relatively simple method offers enough control to work reliably. Despite publishing in Science, I have yet to find a single reference to the work in the published literature, or even any followup experiments. Science 112, p553, 1950 if you want to look it up.
FYI, the same is true of silver halide crystals, and back in the old days they used to judge the extent of ripening by the color of a small sample viewed on a glass slide. The color varied from yellow through green to red, but ended up being obscured when they began using varying amounts of iodide as it gave a strong yellow to red tint to most all crystals.
Ray, I now see those links do not work... try this one by Carey Lea himself:
Originally Posted by Ray Rogers
And another contemporary one - that mentions that Rochelle salt and hydroxide is one of many ways which to make Carey Lea's blue allotropic (collodial) silver:
It seems to me I was making the blue form when silvering the mirrors as a side product.
Thank you for posting this!
Originally Posted by Struan Gray
I am deeply interested, but do not really have the mathematical skills to comprehend it very well!
Last year I read an entire textbook on the phenomena, notwithstanding!
The images you posted compliment the book well.
Actually, there HAVE been several related photographic procedures that seem to use this principal.
I have a small file on this method of color photography as I am planning some experiments in that area... I don't think I was aware of the Science article...
I would love to read it!
Do you have a copy?
What is your interest in this subject?
(if you do not mind my asking)
Last edited by Ray Rogers; 08-29-2008 at 12:09 PM. Click to view previous post history.
Reason: grammer slip