PDA

View Full Version : problem: grey image



Pages : [1] 2

martina.87
01-13-2014, 08:41 AM
Dear photo enthusiasts,
I am a new member of your forum with a 'big' problem. After many years of practice in a darkroom (this includes the use of FOMA emulsion) I've decided to mix the emulsion myself. I followed a very simple recipe:

Solution A:
Gelatin 20g
Potassium bromide 16g
Distilled water 125ml

Solution B:
Silver nitrate 20g
Distilled water 125ml

Everything went well until I developed the first test print. It was going to be a simple photogram to find out how the coated paper works. Unfortunately, all I could get from that were edges of the object: the part of the image that was supposed to turn black came out as very mild grey.

I must add that I used 240 Bloom Pigskin Gelatin.
I went through many threads on this and different forums, but I couldn't find any place that mentions similar problem, or the very basic rules of emulsion making.

Is there anyone who has any idea what could have gone wrong during my process?
I apologize if this issue has been discussed already but I really couldn't find any information (simple enough) that could help.

Martina

dwross
01-13-2014, 09:08 AM
Hi Martina,

Welcome to APUG and emulsion making!

Could you supply a little more information on how you made your recipe? It's likely that it's just a lot slower than you're used to. A couple of possible solutions are more exposure and/or more heat during the emulsion making. Maybe letting the emulsion sit for a bit in the heat before refrigeration. If you washed the emulsion before coating, you may have left too much water so that the emulsion is too dilute. Perhaps coated too thin (?) There are a couple of other possible things to try, but these here a good start.

Best of luck,
Denise

martina.87
01-13-2014, 09:27 AM
Hi Denise,

thank you for your reply. I was wondering about the temperature myself; I am not really able to control it very much: I boiled water in a kettle and used it as water jacket. I have a digital thermometer. but I don't have any special device that would keep the water at stable temperature.
Anyway, I was unable to find any info on how the temperature affects the quality of the final product.

After the emulsion was mixed I immediately filtered it through cotton in a funnel and then I coated it straight on the paper; 1 layer only. I used plain wall paper which I always use with emulsion. I didn't wash the emulsion (don't really know how to do it and whether it is necessary).

I am sorry I must sound really dumb :)

Regarding to the longer exposure: I left a test strip on a direct light for about 30 minutes and I only got the same grey. It kind of looked like an unexposed, but fogged paper.
Thank you for any suggestion.

David Allen
01-13-2014, 09:30 AM
Hi there,

I would suggest that you purchase The Silver Gelatine book written by Martin Reed from Silverprint:

http://www.silverprint.co.uk/ProductByGroup.asp?PrGrp=163

It is truly 'THE Bible' if you want to experiment with this area of photography.

Bests,

David
www.dsallen.de

darkosaric
01-13-2014, 09:30 AM
Hi,

Welcome to APUG :).
I think you need to coat paper two times: once, let it dry, and then again. Try and let us know is it helping.

Regards,

dwross
01-13-2014, 09:39 AM
Martina,

OK, that drills it down a bit. If you coated emulsion when it was very hot, it's likely your coating is far too thin. Let it cool to around 35-40C before you coat.

It's not absolutely necessary to understand what's going on to make a perfectly good emulsion. You can just experiment until you get the results you like and then repeat each time. But, if you'd like a little more info, I can suggest The Light Farm. The best place for you to start would be here: http://www.thelightfarm.com/cgi-bin/htmltutgen.py?content=06Jan2013

d

dwross
01-13-2014, 10:01 AM
Martina,

Oops and apology. Posted the wrong link for you. (Still had it cached from an email I just wrote.) Try this:
http://www.thelightfarm.com/cgi-bin/htmltutgen.py?content=06Jan2013

martina.87
01-13-2014, 10:11 AM
Thank you very much guys. Your help is much appreciated!

David: I have the book but it is still bit too difficult to understand; probably for its vast amount of information.

Darko: I've read about that and I will definitely try several layers. Thank you.

Denise: That is an amazing site with all the info I require. I am sure I will learn a lot from it.

Thank you again :)

m.

Prof_Pixel
01-13-2014, 03:59 PM
Martina,

Having recently participated in some salt printing experiments at the George Eastman House, I can say the paper you use can have a MAJOR effect on the d-min of your prints. Not all acid-free 100% cotton fiber papers are equal. You will probably need to experiment to find the most suitable paper.

Photo Engineer
01-13-2014, 04:17 PM
Martina;

The temperature of boiling water is usually too high for emulsion making. It is 100 C and emulsions are made between 40 and 80C. So, this may be breaking down the gelatin and ruining the emulsion. Try using 50 or 60C and add the Silver Nitrate over about 2 minutes. This may increase contrast.

Also, leaving the emulsion unwashed leaves bromide in it and this is a restrainer. That can lower Dmax.

Last but not least, addition of a tiny amount of Iodide as KI in a 1% solution may help. Based on Silver weight use about 3% of the Iodide for every 160 g of Silver Nitrate.

In any event, this emulsion will be about 3 stops or more slower than a modern enlarging paper, so beware of this big speed difference.

If you need more help, you might try my book available either through the Formulary or Fotoimpex. Ads with URL redirection are here on APUG at the top and bottom of the screen on a rotating basis.

Best of luck.

PE

martina.87
01-14-2014, 01:14 AM
Ok guys, before I try new batch using correct temperature as suggested by Photo Engineer (thank you) I've decided to rule out the possibility of a thin layer; this time I coated the paper with three layers. The results are MUCH better than last time as the surface turned very dark grey - almost black. Not ideal, but much better, so success :)

Prof_Pixel: I've been using this wallpaper for years and I've never had a problem. However, I must admit that when I experimented with other fiber based papers, some of them had shown very different results.

m.

dwross
01-14-2014, 08:32 AM
It helps to understand that the word "emulsion" is a tad over-extended in use. Cyanotype and salted paper (Van Dyke, the 'browns', Pt/Pd) solutions are called emulsions but they are actually very thin liquids that soak right into the paper. The only way to increase the native d-max is to apply multiple coats and the paper type makes a tremendous difference.

Gelatin-based processes (silver gelatin and carbon) sit on top of the paper they are coated on. The thickness of the emulsion can be controlled by both the amount of gelatin used and by the temperature of the emulsion or glop when it is applied to the paper. If you want a thicker coat you don't have to apply multiple layers, you simply cool the emulsion down a bit, or start with a recipe with a higher gelatin content. In fact, each layer introduces coating artifacts -- usually considered flaws, although that is strictly an artistic judgment, not a strictly technical one. As a matter of personal taste, I don't care for sloppy coating, but ymmv. A good emulsion, coated at the right temperature needs only one layer. Paper choice is important. You want a good wet strength and a texture and color that appeals to you, but beyond that, silver gelatin is much more forgiving of paper choice than the thin-only emulsion processes.

Photo Engineer
01-14-2014, 02:28 PM
Coatings made using 5 - 10% gelatin and a doctor blade such as mine or Denise's will deliver a rather precise layer if the emulsion is at about 40C. This is quite repeatable. It will use about 12 ml of emulsion per square foot.

However, I have found that pure bromide emulsions tend to give low Dmax when they are not "finished" with Sulfur sensitization or the Iodide treatment I mentioned above. Pure Bromide is kinda weird that way. So, thinking it over and looking at some of my own results, I have to add this cautionary paragraph.

PE

cliveh
01-14-2014, 02:42 PM
may I ask what you are developing this home made emulsion in? Also what dilution and temperature?

Photo Engineer
01-14-2014, 06:19 PM
Martina, one more question...

Was there much residue in your filter or in the making beaker?

The reason I ask is that this kind of emulsion tends to make aggregates that settle to the bottom or get trapped in the filter. If this takes place, the amount of silver left goes down.

PE

martina.87
01-15-2014, 06:15 AM
Photo Engineer: I am not using the blade; I like the brush look, plus I've never had any problem with it. I used to coat 40" x 60" canvases with my 5" brush. It took some time, but it worked.
Regarding the filtration: I made another badge and I must say that there was quite a lot of residue left in the filter; perhaps I put too many cotton pads in. Do you think that pressing the filter is a good idea?

Cliveh: I use Ilford Multigrade @ 1:9, 20 degree. I guess this isn't the ideal developer, but I have a 5 liters of the concentrate which I don't want to lose, so at the moment I am stuck with it.

m.

wildbillbugman
01-15-2014, 11:32 AM
Martina,
Cliveh asked a very relevant question. I use, as my testing developer, Homemade D19 (recipe in APUG articles. No longer made by KODAK). I use this developer as a rather sever test for fogging. I always get good blacks, and have had to lower my Ag levels simply because I was wasting silver by having more than I needed to get true black. Yet, if I use pyro on the same emulsion, I cannot get true blacks. That is not simply because of the staining characteristics of pyro. The prints are just vet weak.
Bill

Photo Engineer
01-15-2014, 03:11 PM
Martina;

I have used a brush and it gives an interesting look, but when all of these methods are presented in a workshop, the students prefer the smooth quality of a sheet coated with a doctor blade. And, BTW, using a brush may be affecting the amount of emulsion laid down. As for residue, if there is any, this is sucking Silver out of the final material and leving you short of imaging Silver. This should not happen. The formula should be revised.

PE

Photo Engineer
01-22-2014, 02:54 PM
Martina;

Something I forgot to mention earlier. You might want to change to a gold coffee filter instead of cotton. This way you can see any residue more easily and filtration is quick and clean.

PE

martina.87
01-29-2014, 12:56 PM
Martina;

Something I forgot to mention earlier. You might want to change to a gold coffee filter instead of cotton. This way you can see any residue more easily and filtration is quick and clean.

PE

That sounds interesting. I managed to try different surfaces and I also managed to keep the temperature as close as possible; the results remain the same as at the beginning. I think that it could be caused by wrong filtration.
I wonder if paper coffee filter would do the same job as the gold one.