Our newest results.
We got an access to a lab at our university that has a commercial corona treatment unit. That worked very well for subbing PET and we were able to make coatings that survive any normal process perfectly.
We made a new emulsion, and this time it's fogless!
We used pig skin food grade gelatin and home-made silver nitrate again and used a modified version of PE's "A real formula" topic. We did the addition of silver in a similar way that is described at Jim Browning's website, but speeded up a bit.
We used a simple conductivity meter to measure wash water compared to conductivity readings of NaBr solution of 0.030 g/l, and found out that the washing step was quite quick, less than one hour. For final wash, we used NaBr at 0.100 g/l in wash water.
We used erythrosine now at 150 mg/mol of silver. Emulsion is now much more red (but still quite orange) than last time when we used 50 mg/mol.
ISO speed estimate is 25, when developed in XTOL 1+1 for 5 minutes at 24C. This was estimated by comparing to Agfapan APX100, developed in XTOL 1+1 for 7 minutes at 24C. When our film is exposed from the same stouffer step wedge but two stops more, it gives about the same shadow speed at the first visible step, thus being ISO 25. However, the toe is somewhat softer and it seems it's better shot at EI 16 or so.
Fog is almost nonexistent, like in any slow BW neg film.
Contrast is quite high. Maybe we should use the exact silver addition numbers in Jim Browning's document. Now we speeded it up by about 20%. This emulsion might be best shot at EI 16 and developed for only 4 minutes or so, with less agitation.
Film is flexible and runs well in Mamiya 7. we added sorbitol, reduced glyoxal to half and reduced blade opening to about 200 um compared to 300 um before.
6x7 film scan - unfortunately I got only one full image since I taped the film at an incorrect position in the backing paper. Big version: http://www.students.tut.fi/~alhonena...ga_1200dpi.jpg
Print on Kentmere 24x30 cm (9.5"x12") glossy. Contrast filtration of 0 ½. Print looks quite good, scanning is difficult as always. Big version:
Shadows on the left are blocked, but I metered with Mamiya 7 set at ISO 25 from the sunlit grass, so no wonder. The light was very hard. It seems from the Stouffer scale that the emulsion has 8 stops of good exposure range.
We are quite happy of these results!!! :cool: :munch: :D
To Be Continued!
That's great! Congratulations.
Quite marvelous! Very much looking forward to the next chapters. Keep 'em coming! (But make sure to enjoy at least a few summer days :).)
Good work! Keep it up.
Excellent work, great to see such a great result.
Great work. Congratulations.
At that concentration of NaBr after the wash, at 10 deg C (a good wash temp), the vAg would be about +37 and at 40 deg C (a good coating temp) it would be about +67 mv. This is a very good position for the final emulsion. I often aim for about +50 mv.
How did you sensitize it with hypo (time and temp)? I use about 100 mg/mole of Sodium Thiosulfate Pentahydrate for 60 minutes at 60 degrees C. This would give you more fog but also more speed. Also, Erythrosine can cause speed losses if used at too high of a concentration so it must be "just right".
The corona treatment sounds as if it is just about near perfection now. Thats wonderful.
No hypo sensitization yet. This gelatin probably have some sulphur compounds as the speed and contrast is so good without any sensitization. I have a plan for sensitization step and I hope I am able to try it this week.
Do you have a photo or schematic of the corona discharge unit that you can show?
Also, can you describe your coating method in any detail?
I wish I had a schematic of the corona discharge unit mentioned; then I could replicate it. It is quite small, with a working area of about 20x20 cm that seems to be made of about 1 cm thick Teflon(?). It has a roller that has the anode(?). The roller is used by hand and is about 3 cm of diameter and of white plastic that didn't seem like Teflon. Hard to say. The anode(?) is inside the roller.
It has a wattage meter from 0 to 200 watts. It showed approx. 20-40 watts during the treatment. It also had a knob called "treatment level" from 0 to 10. Level 5 wasn't enough to make PET hydrophilic but 8 was :). After treatment, a small amount of water forms a very even, thin layer on the sheet. A huge difference compared to untreated areas as I run water over the sheet.
I built a HV probe so I could measure the output from the unit with oscilloscope and then replicate it. But I don't know when we'll get next chance to see and use the machine at the lab.
We still use the same blade we made when we started; I have posted pictures of it: http://www.apug.org/forums/forum205/...tml#post866943 . The gap is about 200 um. I tape the PET sheet on the glass plate, use a 50 ml syringe to squirt some emulsion in the front of blade and give it a go. Then I put the glass plate + the sheet in a refrigerator for a minute or two and then let dry for 24 hours at room temp. I use some masking tape to secure the sheet on the glass plate so it won't curl during drying.
Thank you everyone for encouraging words!