Pouring plates, big ones.

[RobertP]

PE, Yes the edges are roughed with a stone or file. I've actually seen guys just rough the edges with another piece of glass. For ambrotypes this is sufficient but if you are doing a glass negative and redeveloping the negative to build density then the pyro in the developing solution will cause the collodion to shrink and at times lift it from the glass. By subbing I mean that a thin coat of albumen is put down on about 1/8" around the surface edge of the plate. There's nothing worse than getting a nice plate and then watch the collodion slide off during development or intensification. I rough the edges and sub the edges with albumen and have never had one lift. I take one egg white and dip a Q-tip in distilled water and then in the egg white and sub the edges, let it dry for a minute and the plate is ready to pour. That's not much effort to insure the collodion don't lift.

 

[Photo Engineer]

Robert;

I got some sample plates from the Formulary, and I noticed that they are all polished on the edges. This probably puts a tooth on the edges just as we are describing as the plates are precision ground to exact square and size.

PE

 

[Anton Lukoszevieze]

I rub the edges of my plates with a piece of glass, works every time.

 

[RobertP]

PE, That is probably exactly the reason and that is to give the plate tooth. This is not necessary for tintypes, (japanned tin or trophy aluminum) but for glass it is a must. Also for albumen printing or any contact printing process, the albumen subbing on the edges isn't noticeable on the final print. Or let me say if it is I can't see it.

 

[Photo Engineer]

Interestingly enough, it was not done to commercially produced plates. As I said above, the plates were cut from a large sheet of glass after coating and this would preclude any edge treatment that would help.

PE

 

[RobertP]

PE, In some of the old literature it talks about using albumen to sub the entire plate. The formula for using albumen to sub the entire plate is: Two large egg whites to 1 liter of distilled water. This is poured on and flowed just like you would the collodion. It then could be cut to any size desired. We also could be comparing apples to oranges here. I'm talking about wet plate collodion and not dry plates. But you could flow albumen on a large plate and let it sit for days or longer before cutting to size and using it to flow your wet plates. I guess that would hold true for coating a dry plate emulsion also. Albumen plates should be used within a few days or stored properly because in hi humidity yeast in the air can react with the albumen and cause contamination spots.

 

[RobertP]

Also let me add before you do anything with the glass plates you must make sure they are extremely clean. I use to use "Glass Wax" but it is no longer available. Now I use a "Whiting" mixture which is nothing more than 40 grams of calcium carbonate mixed into 50 ml of distilled water and 10ml of 190 proof grain alcohol. Works great.

 

[Photo Engineer]

I am talking only about dry plates. They were not subbed AFAIK nor were the edges prepared in any way. The large 30x40 sheets were coated, dried and then cut into 4x5, 8x10 and etc. There were other large plate sizes besides 30x40.

A special machine was manufactured that cut the coated dry plates, and also removed the glass dust. All of that technology has been essentially lost.

I clean my plates with Potassium Dichromate-Sulfuric Acid grease removal solution after a good wash in detergent. I rinse in DW and let air dry before coating.

PE

 

[Kirk Keyes]

Potassium Dichromate-Sulfuric Acid

It's an excellent glass cleaner and I remember the days that it rule them all in chemistry labs.

Now, it's considered environmentally hazardous and not used in most lab applications.

 

[Kirk Keyes]

I am talking only about dry plates.

Do you know if the machines cut the gelatin as it scored the plates? It seems like you would have to do the scoring from the emulsion side to get it to work.

 

[wildbillbugman]

It's an excellent glass cleaner and I remember the days that it rule them all in chemistry labs.

Now, it's considered environmentally hazardous and not used in most lab applications.

I have read that some people soak their glass plate in a fairly concentrated solution of NaOH. This puts a micro-tooth on the glass and creates a mono-molecular layer of sodium silicate. The later can benefit adhesion.
Bill

 

[Photo Engineer]

I use so little Dichromate that it is not a problem. It can be reused over and over for this application. The Sodium Hydroxide should work, but IDK how fast it will react with various types of glass. It can make some glass translucent.

PE

 

[wildbillbugman]

Hi,
I would think that soaking the glass plates in NaOH would also serve to smooth out the edges without having to file the edges or sub the edges.
Bill

 

[totalamateur]

Ajax and Green Scrubby

When I pour my plates, I wash them with Ajax or Comet and scrub the heck out of the edges with a 3m green scrubby. The emulsion I did this with was always a knox-gelatin emulsion (but never again), and I never had any problems with adhesion, no hardener used. Stupid Knox Gelatin will melt right off the plate, though.

To get an even coat, I put all my plates in the oven and heated them to about 120, just hot enough to where they are almost uncomfortable to hold, then keep them in a stack as I pour, so that the plates behind the ones I'm coating smooth out the temperature across the top plates and keep my fingers from causing thick spots. Unfortunately, the last one generally comes out uneven. If I were smart I'd have one extra glass plate that I didn't coat.

I think for big plates, you could make a plywood jig to hold them with a tripod mount on the bottom, so you wouldn't have to hold the weight as you tilt it around, just swivel your tripod head. Several layers of warm glass under the top plate should keep it warm enough until the emulsion is completely coated. The only issue then would be to perfectly level the plate once it's been coated. this was the issue that i had, apparently there isn't a level surface anywhere in my house. Maybe a couple of spirit levels glued to the side of the jig would help.

I'm no expert, just m 2 cents.

 

[Kirk Keyes]

Unfortunately, the last one generally comes out uneven. If I were smart I'd have one extra glass plate that I didn't coat.

Get some ceramic floor tiles (they come 12x12 inches) and put them under your stack of glass plates. The ceramic tile should hold the heat for a while and help keep you glass plates warm longer.

 

[Ray Rogers]

To get an even coat, I put all my plates in the oven and heated them to about 120, just hot enough to where they are almost uncomfortable to hold, then keep them in a stack as I pour, so that the plates behind the ones I'm coating smooth out the temperature across the top plates and keep my fingers from causing thick spots.

How are you guys (it's not just TA) putting glass plates in ovens?
(Are you using some kind of rack?)

How are you stacking the plates without worry of scratches,
& keeping the surface level while moving them to their setting areas?

 

[totalamateur]

I just set them on the rack, which is clean. They are never in the oven with the emulsion on them, I just heat them up before taking them to the dark room to coat, hence the need for multiple plates (or a ceramic tile, now that Kirk mentions it) to keep the heat in.

The oven isn't for drying, it's so the emulsion doesn't set up when it hits a cool plate, making the coating uneven. My kitchen isn't light - tight, so I can't really put coated plates in the oven.

I've been lazy so far as getting a level surface, but my next plan is to put a chunk of plexi or plywood on top of big balls of modeling clay, one on each corner, and using bubble levels while squishing the balls of clay to make a level surface on my workbench.

I loke the idea of coating the edges of the plate in wax of some other substance to keep the emulsion from running off the side unexpectedly. Maybe a strip of masking tape perpendicular to the edges would do the trick. that could help with a larger warmed plate, since you would have a little more time to work the emulsion around the surface before it set-up.

 

[totalamateur]

I was wrong

Well, I poured a batch of plates tonight and found that you do not want them to be all that hot, The emulsion was too thin, and didn't coat very well until everything cooled down a bit. So, my description of about 120 degrees was quite incorrect.

 

[Photo Engineer]

The optimum that I have found over the years is to have everything at about 110 deg F with about 5 - 10% gelatin.

PE

 

[keithwms]

When I want a *really* uniform, bubble-free coating of photoresist on a plate I put it in a spin coater. I have a coater that can handle plates up to 9". Now, I wonder if something like a potter's wheel might be able to handle really big plates. My spin coater has a vacuum that holds the plate down firmly; with a potter's wheel I guess you'd have to glue it, or maybe design some suction cup or something, or make a holder for the plate that can be screwed onto a platten. Anyway, for emulsion it'd not take much speed. For my photoresist we have to get up to 1000+ rpm, but that's for submicron films. For ordinary films with good uniformity and if you don't care too much about the thickness, I am thinking that you'd not need more than ~20 rpm. Say, how about a good old record player....

Spinning would also save a lot of emulsion, you can make a thing that catches what flies off and recycle it.

 

[dwross]

I find that even 110F is too warm for coating. I need to keep my emulsion in the 34C-36C/~95F range for optimum coating, with the glass plates at about 70F. Since I'm quite sure Ron's results are spot-on for his emulsions, it just goes to show that people need to determine their own best conditions. Don't assume too quickly that your emulsion or coating technique is flawed. A very simple tweak of your workflow may be all that's needed to get great results.

Keith: A spin technique may work well for collodion. If I understand that process, coating thickness doesn't matter so much. Not so with silver gelatin. Too-thick coating won't develop evenly and/or will be too dense to print, and too-thin will result in flat negatives (not wasted, fortunately, if you are willing to go the Photoshop => digital route). As for catching emulsion that flies off, that too presents problems. I think the flying emulsion would cool and set up almost immediately unless you were able to collect it in a heated container and return it the original batch for the immediate coating of your next plate(s). Still, it's an intriguing idea, even if it's a bit more complex (and messy!) than required for the home darkroom emulsionmaker. There are probably any number of engineering wizards here on APUG who could have a lot of fun with the concept.

d

 

[keithwms]

Keith: A spin technique may work well for collodion. If I understand that process, coating thickness doesn't matter so much. Not so with silver gelatin. Too-thick coating won't develop evenly and/or will be too dense to print, and too-thin will result in flat negatives

The really good thing about spinning is that you can control the thickness via the spin rate. I think if the viscosity of the emulsion is reproducible then it should be possible to measure spin curves that tell you what rpm and time to use to achieve whatever thickness you desire.... from thin to ultrathin. Thicker is actually harder; to get really thick films we usually just spin more than once. But I am thinking that in this case you want ~microns of thickness and that should be easy.

About reclaiming the fly-off, yeah that may be wishful thinking But anyway one of the great advantages of spinning is that you can use minute amounts of material to coat the surface very uniformly. A drop of standard viscosity photoresist easily coats a 6" wafer, for example.

I'll give it a try if/when I have time.

 

[Ray Rogers]

I just set them on the rack, which is clean.

That is what I don't follow...
I bake bread in my oven; I have different trays, metal, ceramic and glass, but I would not think of putting glass plates down on any of them...

I thought you might be putting them in a rack as when drying, but the ovens here are much much smaller than where you folks are... so it would be kind of crowded... not to mention being sented wth Pizza or Gingerbread.

 

[Photo Engineer]

Ray;

The clean uncoated plates are warmed in the oven before coating.

They are coated warm and then chilled. When chilled they set up and can then be placed in a cool dark drying rack!

PE

 

[Ray Rogers]

About reclaiming the fly-off, yeah that may be wishful thinking

Well, if you have a lot of material and you really want to, you don't actually need to pour it... Just scoop it up in what ever condition it is in and put it away safely for the next day of coating.

But this probably won't work very well if, as you mentioned above, you are coating by the "drop".

Ray

(thanks for the pdf btw!)