hazy 2-color

[Joe Farina]

Thank you Martin. That makes perfect sense, and must be the reason, especially since the amount of chromate is extremely small compared to regular DCG. What I would really like at this point is a reliable way of pre-hardening the coated plates. Earlier, I had some erratic results with formaldehyde vapor in a closed container (either liquid formalin or solid paraformaldehyde), and I'm thinking of trying this again with the new gelatin.

[Steven]

Color DCG is a fairly tough road, at least I've found it so. It would help enormously to compare notes with others, but I don't know of a single person currently working with MBDCG.

Hi Joe,

I'm shooting an exposure test plate right now. It's a dip & shoot, based on the chemical ratios proposed in the paper by Jianhua Zhu et al.

I haven't used any MB, just the R6G as I'm only shooting at 532nm. I don't have TMG as you know, so I'm giving Guanidine carbonate a try.
I'm just trying to experiment with the ratio of chemicals to water for the sensitizing solution. I did a few small test strips yesterday, not for exposure, but to just measure the absorption at 532nm and to find out how much dipping time is needed to get the sensitizer right down into the gelatin. I found that there was not much benefit with a dip longer than ten minutes as the absorption flattened out. I'm using pig gelatin with a coating of about 8µm - 10µm, so I have biased the sensitizing solution's PH a little higher, at about 10. I have also cast a couple of plates with pig gelatin, but with added Guanidine carbonate to bring the PH up to 9.4. I did manage to cast another couple of plates using 300 bloom bovine gelatin to see is there is any difference in the results.

What absorption do you get with your plates at 532nm?
I measured my plate (at Brewster's angle) to be about 30% which may a little high.
There is an absorption graph in the Jianhua Zhu paper, but I suspect that it was measured at normal incidence.

Oh, time to do another exposure.

Steven.

[Joe Farina]

Hi Steven,

Glad you're doing some experimentation.

30% absorption is too high. I did some absorption tests for Jeff's MBDCG (no R6G and with red light only) on a 25 micron layer, not at Brewster's angle. The loss from the glass reflection was 10% and the absorption loss due to the MBDCG layer was 7%. So 83% was getting through (17% losses total). The addition of R6G in the panchromatic formula would cause some additional loss, but in Zhu's formula, it's used at half the concentration of the MB. Although I haven't done absorption tests for R6G+MBDCG, I can tell from the visual appearance of the layer that transmission is comparable to plain MBDCG.

I was surprised at the effectiveness of R6G with 532nm light. Very little is needed. When I expose at 532/633 using Zhu's dye ratios, I have to use almost twice as much power at 633nm (for the MB component) compared to 532nm (for the R6G component).

Good luck, and I'm looking forward to hearing about your progress.

[Steven]

Thanks for the info Joe.

I suspect that you are right re only getting about 70% of the light through the plate, but I will give it a go. I can always add more H2O to the solution.

As a point of reference, I measured the transmission of a plain coated gelatin plate (again at Brewster's) and there was no measurable difference between no plate or a gelatin coated plate inserted in the path, which is what I expected to see. I also measured the power of the transmitted beam through a 3% AmDi 1 minute dipped sensitized plate (again at Brewster's), it was measured as 95.3% of the indecent beam power. Obviously, the optical path length through the gelatin will be longer at Brewster's, so using a 10µm coating will give a path length through the gelatin of approx 17.9µm.

I have revisited Zhu's paper and taken a closer look at the graph (fig 1) on the bottom of page 3.
The absorbance at 532nm looks to be about 0.225
According to Wiki: http://en.wikipedia.org/wiki/Absorbance
Using the above figure of 0.225 and the log10 base formula, punching numbers in my calculator, I get a transmitted beam that is 60% of the indecent.

What sort of exposure (mJ/cm²) at 532nm are you using Joe?
I shot my first test plate this morning, with 25,50,100 and 150mJ, ref beam only measured.
I'm shooting a plain sheet of aluminium.
I will shoot my second plate tonight with 200,300,400 and 500mJ exposures.

I intent to process the plates with a chilled solution of sodium metabisulphite, tap water wash until clear, swelling/wetting bath and two IPA baths.
The swelling and IPA baths will be at ambient.
I will see what come out

[Joe Farina]

I have revisited Zhu's paper and taken a closer look at the graph (fig 1) on the bottom of page 3.
The absorbance at 532nm looks to be about 0.225
According to Wiki: http://en.wikipedia.org/wiki/Absorbance
Using the above figure of 0.225 and the log10 base formula, punching numbers in my calculator, I get a transmitted beam that is 60% of the indecent.

Hi Steven,

I didn't take the time to convert Zhu's "absorbance" figures in the graph to a percentage of transmitted to total incident light. Honestly, I don't know how it's done. It's difficult to imagine that 40% of the incident light is being absorbed at 532nm, though. Maybe someone else will chime in with a 3rd opinion or some clarification on Zhu's chart ("Figure 1, The spectral absorbance of a red-sensitive gelatin and our panchromatic gelatin").

I think we need to keep in mind that Jeff's MBDCG and Zhu's R6G+MBDCG are quite similar to each other (exactly the same, except for the addition of R6G), and these appear to be substantially different from the method you're using. So it's difficult to compare the two, or make any definite suggestions. The amount of light I use at 532 for Jeff's/Zhu's system is about 14mW of light spread over a 5 X 5 inch plate, for about a 30 minute exposure.

[Steven]

Hi Joe,

I must admit that I had never given the term 'absorbance' much thought before.
I just thought a figure of 0.225 would mean that 22.5% of the light would be absorbed by the emulsion.
It was only after visiting the Wiki page today, that I realized my error.

Thanks for the info re your exposure.
If the 14mW is just expanded to cover your 5" x 5" plate, that would work out at about 156mJ cm² with the 30 minutes exposure.

I suspect that my plates will be considerably deafer.

I did try a dipping solution that matched Zhu's paper, but using the carbonate instead of TMG, and without gelatin.
I realised later, that I should have been looking at the formulae concentrations in respect of the gelatin concentration, not the H2O.
I did shoot a test plate last week, but there was no hologram. The plate was only slightly milky, so I upped the swelling bath temperate.
I got branches of crystals all over the plate while under the hair dryer. Eventually they cleared leaving a milky plate, but again no hologram.
I did inspect the plate under my microscope, and did spot just a few small areas near the edge of the plate that showed some cross linking, they just look like small coloured worms. My current sensitizing solution is stronger than Zhu's mix as the gelatin will not be fully swollen when it's removed from the dipping solution. The funny thing is that the gelatin does not dissolve like it does when sensitizing in an AmDi dip.

Steven.

[Joe Farina]

Hi Steven,

I'm embarrassed to admit that I never learned to calculate mJ or uJ exposure levels, so thanks for doing it. Wow, my emulsion is slow! That almost sounds like quoted exposure levels for MBDCG without an electron donor. Nothing compared to Jeff's quoted 50mJ or Zhu's even lower levels. On the other hand, I could have been over-exposing lately, because I've been working on other parameters instead of exposure levels. To get a decent image in my system, I'm under the impression that over-exposure is better than under-exposure (but over-exposure does definitely result in a dimmer image compared to the optimum exposure).

That's a very interesting technique about observing crosslinked gelatin with a microscope! I've never heard of it. Can you provide any further details. Thanks.

[Dinesh]

Honestly, I don't know how it's done.

I must admit that I had never given the term 'absorbance' much thought before.
I just thought a figure of 0.225 would mean that 22.5% of the light would be absorbed by the emulsion.
It was only after visiting the Wiki page today, that I realized my error.

It depends on what's meant by "absorbance". If, by "absorbance" is meant OD, then you use the formula in the wiki. In this case,

I(1) = 10e(logI(0) - A).

But, be careful that the absorbance is given as an OD, as opposed to simply a percentage loss. If the absorbance is OD = 0.225, this is very different from absorbance = 22.5%. Also, you need to determine whether this figure is per unit distance (units!) or whether the paper mentioned a specific emulsion depth and measured the loss at that depth. In other words, is this figure of 0.225 mean a loss of 0.225*I(0)/mm ? Remember that light is being absorbed as it passes through the emulsion, so the absorbance is an exponentially decaying figure. One other factor to consider is the variation of density in the emulsion. These absorbance figures usually refer to a uniform emulsion with uniform density. If there are non-uniformities or any other scattering centres in the emulsion, then these losses need to be taken into account.

[Steven]

Many thanks for your input Dinesh.

"It depends on what's meant by "absorbance". If, by "absorbance" is meant OD, then you use the formula in the wiki. In this case"

Yes, that's why I had to look it up. It can be confusing. From the wiki page:
"In physics, the term spectral absorbance is used interchangeably with spectral absorptance or absorptivity. In this case it has a slightly different meaning: the fraction of radiation absorbed at specific wavelengths"

There are also two formulas, one using base 10 log and the other using natural log (ln)

From the paper:

"The depth of photosensitive layer is about 18μm"

"Fig.1 gives the spectral absorbance curves of an ordinary red-sensitive gelatin and our panchromatic gelatin, which are recorded with a high-resolution
SHIMADZU UV-Vis recording spectrometer (model UV-2100)."

They don't say per unit depth, so I assume they were measuring through the whole 18μm photosensitive layer.

The Zhu paper Joe and I are referring to can be found here: http://sutlib2.sut.ac.th/sut_contents/H ... 636_40.PDF

Steven.

[Steven]

Hi Steven,

I'm embarrassed to admit that I never learned to calculate mJ or uJ exposure levels, so thanks for doing it. Wow, my emulsion is slow! That almost sounds like quoted exposure levels for MBDCG without an electron donor. Nothing compared to Jeff's quoted 50mJ or Zhu's even lower levels. On the other hand, I could have been over-exposing lately, because I've been working on other parameters instead of exposure levels. To get a decent image in my system, I'm under the impression that over-exposure is better than under-exposure (but over-exposure does definitely result in a dimmer image compared to the optimum exposure).

That's a very interesting technique about observing crosslinked gelatin with a microscope! I've never heard of it. Can you provide any further details. Thanks.

Working out mJ/cm² is quite easy.
You have 14mW of laser power spread out over a 5" x 5" plate.
That works out at approximately 161.3 square centimetres.
Each square centimetre of your plate receives a power density of 14mW divided by 161.3, giving approx 86.8µW per square centimetre.
The unit of energy (well one of them) is the Joule. One Joule is one watt for a period of one second.
A 30 minute exposure is 1800 seconds, using the figures above, 1800 X 86.8µW = 156.24 mJ/cm²
The above figures assume that the whole 14mW is spread out over the 5" x 5" plate and no more, and after the spatial filter (if you are using one).

My laser power meter measures power/cm² directly.
I'm using the OPT101, the circuit is described here:
http://redlum.xohp.pagesperso-orange.fr ... meter.html

It does look like you are not getting the sensitivity indicated in Zhu's paper, but that may be down to the gelatin or processing (F5 fixer?)
It may be that you are not getting the full 14mW at the plate? - see above.

Re seeing coloured worms through my microscope.
I usually observed these on a hologram that is very bright/broadband and they are more easily seen at the very edge of the emulsion particularly, where the emulsion is much thinner than the main plate area. It is if you are looking through a bunch of different coloured wool, it may be my cheap Edmund microscope causing the colours though. When you change the focus, it is as if you are focusing on a different thread of the bunch of wool.
On a strong DE area, when you change focus, you can follow the threads through the depth of the emulsion, they also change shape as you do this.
Imagine focusing on a coiled hosepipe in a bucket with a limited depth of field.
It only works on an uncapped hologram, otherwise you can't get the objective lens close enough to the emulsion.

I have attached a couple of snaps taken through the eyepiece with my hand held webcam using an uncapped sample plate.
worms.jpg was taken at the edge of the plate where the coating is very thin.
worms2.jpg was taken at the edge of the emulsion. you can see a diffraction pattern in the lower left, the "worms" are in the upper right.

Time to power up the 315M-100

Steven.