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dwross
08-27-2008, 09:22 AM
The subject of Carey lea silver comes up from time to time. It seems to be a part of the history, lore, and technology of emulsions, so at Kirk's suggestion that we start a thread devoted to the subject, I lead off with this very interesting article.

http://www.chemheritage.org/pubs/ch-v24n4-articles/feature_careylea_print.html

Happy reading,
Denise

Photo Engineer
08-27-2008, 10:21 AM
Just to put things in perspective, Carey Lea Silver (CLS) is used as the yellow filter layer in all color photographic products except negative color papers. I have formulas for this and for a black AH layer that use Lea's methods. I hope to reduce them to usable form soon for posting if there is interest.

PE

Kirk Keyes
08-27-2008, 03:30 PM
Thanks for starting this, Denise. That was a good page you linked to.

Here's a couple I found.

A nice, vintage report on colloidal silver and it's preparation by Carey Lea himself:
http://books.google.com/books?id=K5M...lver#PPA337,M1

And another one from the same era with more details:
http://books.google.com/books?id=zZM...otropic+silver

Photo Engineer
08-27-2008, 03:39 PM
Except for use in image transfer, colloidal silver has little other use except in color photography as AH and yellow filter layers. It is not used in B&W photography outside of Polaroid type B&W transfers.

The chemistry is a bit exotic and the equipment required and steps required are complex. For example, to isolate this very fine silver "mud" as it was called, a centrifuge was used to wash the colloid. Filtration was impossible due to the fact that it clogged the filters. So, there are a whole host of things that are not disclosed in the early patents and writeups.

Kirks earlier references did not give specific formulas, and the references above do not work.

PE

dwross
08-27-2008, 04:20 PM
Kirk,
I'm looking forward to reading those links. I can't imagine why they don't work. I'm about to try one myself. Fingers crossed...

http://books.google.com/books?id=X_YQAAAAIAAJ&pg=RA1-PA482&dq=carey+lea#PRA1-PA482,M1

Also, if any of us move beyond the point of pure historical interest and find a good use for colloidal silver, there seems to be commercial sources. I don't know if they are identical to a homebrew CLS, but it might be a good (although expensive) starting place.

http://www.spectrumchemical.com/retail/product.asp?catalog_name=Chemicals&product_id=6583805

Denise

Barry S
08-27-2008, 05:00 PM
I used to make colloidal gold for research purposes and it was definitely a tricky business. I don't know about silver, but there were a lot of poor methods out there for gold. The biggest issue with poor preparations was a wide dispersion of particle sizes--which usually caused problems with the downstream application. A good colloid is the size you want it to be with a fairly narrow spread in particle size. A centrifuge is necessary for concentrating and washing the colloid and a scanning spectrophotometer is used to assess the particle size and spread.

dwross
08-27-2008, 05:40 PM
I've always wanted to own a centrifuge.:) After seeing Kirk's collection of totally cool used lab equipment, it's almost tempting, and doesn't seem that unreasonable.

http://cgi.ebay.com/IEC-INTERNATIONAL-EQUIPMENT-CLINICAL-CENTRFUGE-4-POS_W0QQitemZ270269101157QQihZ017QQcategoryZ26232Q QrdZ1QQssPageNameZWD1VQQcmdZViewItemQQ_trksidZp163 8Q2em118Q2el1247

Photo Engineer
08-27-2008, 06:07 PM
Well, to connect this all to the Polaroid thread we started from, here is a simplified view of how Polaroid B&W works.

One sheet is a negative film the other is a sheet of paper with baryta or titanox overcoated with a layer of neutral colored colloidal silver that is so finely divided and so low in coating weight that the dmin is not turned gray or discolored.

You take a picture and spread a goo between these two sheets. The goo must be bubble free and is composed of a fast acting monobath. The goo must be spread evenly by means of rails and rollers to get an even coating.

As the negative image develops, the fixing agent dissolves the positive image which is silver halide and it diffuses to the reciever sheet with the colloidal silver. There, the colloidal silver acts like a uniform latent image waiting to happen and the dissolved silver halide begins to form a positive silver image. BINGO! Positive print!

Now, the image that forms is colloidal, has a silver halide solvent present, and is therefore subjet to bronzing and fading so you have to coat it with something to "tone" it. This is the little applicator that Polaroid supplies.

Now, where does the speed come from? Assuming a 50 ISO negative, if it were coated on paper, it would be ISO 100 due to back reflection and due to the chemistry involved, you mainly get the toe silver from the negative which is about ISO 100, you can get a print of about ISO 200 from an ISO 50 negative emulsion.

That is a short description of the process.

Colored colloidal silver can give colored (toned) images to start with. Non-uniform colloids can give uneven or blotchy images. So, the silver must be neutral and very low in coating weight per unit area and should be the finest of all possible colloids.

PE

Kirk Keyes
08-28-2008, 01:14 AM
Denise - I think we had that model centrifuge in high school, 25+ years ago. But there are a lot more at less expense you could get.

Photo Engineer
08-28-2008, 09:53 AM
I used to use an old hand cranked version in HS.

PE

dwross
08-28-2008, 10:48 AM
I used to use an old hand cranked version in HS.

PE

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!

:) 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).

Kirk Keyes
08-28-2008, 11:46 AM
I used to use an old hand cranked version in HS.

PE

THere's one of those on ebay right now.

Barry S
08-28-2008, 01:46 PM
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.

Photo Engineer
08-28-2008, 03:59 PM
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.

PE

Kirk Keyes
08-29-2008, 01:02 AM
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.

Ray Rogers
08-29-2008, 06:12 AM
One of the links I gave above gave Rochelle salt (potasium sodium tartrate) as one of the reducing solutions

???

Struan Gray
08-29-2008, 07:38 AM
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.

Photo Engineer
08-29-2008, 09:52 AM
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.

PE

Kirk Keyes
08-29-2008, 10:20 AM
???

Ray, I now see those links do not work... try this one by Carey Lea himself:
http://books.google.com/books?id=K5MOAAAAIAAJ&pg=PA337&dq=carey+lea+allotropic+silver#PPA342,M1

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:
http://books.google.com/books?id=zZMUAAAAYAAJ&pg=PA282&dq=carey+lea+allotropic+silver

It seems to me I was making the blue form when silvering the mirrors as a side product.

Ray Rogers
08-29-2008, 01:07 PM
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.


Thank you for posting this!

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)

Ray