Safelights during emulsion making - I do not get it!

[rwhb12]

We all know that we use a safelight of a particular frequency to avoid exposing emulsions or negatives. But we tune those lights to an area that we know our emulsion is not sensitive too. So why are people mixing emulsions in the dark or using IR goggles, if we can use, say, a narrow band 598nm safelight? Is it because we do not know what the emulsion is sensitive too? If so, maybe someone can tell us which chemistry needs which wavelength of safelight?

Russ

 

[dwross]

Hi Russ,

I'm not aware of anyone mixing emulsions in the dark or with IR gear, unless they are making a panchromatic emulsion. You have to do panchromatic sensitization in the dark, but for the home darkroom, that's best as a step that comes after an orthochromatic emulsion is made, coated, and dried. It's not sensitive to red light. That's why you can do regular printing with a safelight. I recommend small red LED's. This is where modern has got "traditional" beat. Nothing worse that a cheap old red paint covered incandescent bulb with a bunch of tiny chips in the paint!

 

[Photo Engineer]

Yes, Denise is absolutely correct. Use red safelights until you get to pan sensitization.

PE

 

[rwhb12]

Thank you for the quick response Guys!

But with Pan emulsions, even then are we saying that all the silver halides can be over exposed with a single band of light of say 589nm, thus corrupting all other frequency responses of the crystals?

Russ

 

[dwross]

rwhb12,

Did you change the wording and direction of your first post? The physics of optical absorption is probably beyond the scope of this forum. It's an interesting subject (at least what I can grasp of it!) but there are still a lot of unknowns, and details down to the nm are important only on a theoretical basis -- useful for research on absolutely pure, single crystal emulsions of a precise given age. I can recommend "The Theory of the Photographic Process" 4th edition, edited by T.H.James, 1977. Even that is probably dated science by now.

Get a nice red LED and start making emulsions!

 

[Photo Engineer]

With a pan emulsion, a red light can fog the red component.

There are 2 ways to get pan sensitivity. Mix 3 emulsions each sensitive to B, B/G, and B/R. A red safelight will fog only the B/R component. However, if you use a pan dye, then red light exposure fogs everything. You see, then the emulsion is B/G/R sensitive all at the same time.

So, the results depend on the method of sensitizing. At the present time, I know of no dye that will give pan sensitivity on its own. They are used, but not available to us AFAIK.

PE

 

[rwhb12]

Thanks guys. Just finished making a batch of emulsion. Everything that could have gone wrong, went wrong, including dropping the container on the way to the fridge! Maybe I might get a result....

russ

 

[dwross]

Congratulations! You really can't call yourself an emulsion maker until you've made a truly grand mess!!

 

[removed account4]

 

[kb3lms]

Hi rwhb12,

You've got to make a few messes and you'll make some batches that do absolutely nothing! Just part of the fun.

Just curious, what sort of emulsion are you making?

-- Jason

 

[rwhb12]

First emulsion

I am following Mark Osterman's GEH emulsion course after attending the GEH course in 2013. It has taken this long to get the equipment together, with the glass to fit wooden plate holders (found in the US) for my 10 x 8 being the last.

Other than the battery failing in my timer, finding green lights on my stirrer controls, not having enough light to see by and knocking over some of my glassware, spilling some of my silver nitrate, loosing my magnet from the stirrer in the emulsion (this is now firmly set in the fridge inside the emulsion), realising that the nylon gasket on my ceramic pot lids are clear and will transmit light, taking ages to weight .4g of fine powder on my balance scales (how do you remove a few grains from a pile?), having my beaker floating in the water bath (weighed down with large bottle), getting emulsion on my figures (now looks like some weird tattoo) and shooting my silver nitrate solution with no timer and of course dropping the whole finished product. Everything went fine!

I now have to noodle and wash in the bathroom and rig up a light tight wash system! HEY - idea - I will wash with my Jobo developing tank and CP2 that would work! I can fill the tray with iced water and change the wash water in the dark!

Now it is GOOD to talk!

Russ

 

[Photo Engineer]

You can remove a few grains with clean tweezers, or by tapping the pile onto another surface. Taps will remove down to individual grains if you gain enough experience. As good as tweezers.

The green lights will be no problem with Mark's emulsion.

As for all of the others Russ, BTDT! It is painful, but it happens to everyone.

PE

 

[kb3lms]

Washing in a developing tank? Interesting idea. I've been using one of those cocktail shaker things. It's insulated and doesn't leak a bit. Never have been brave enough to risk it's light tightness although I think it would pass. Besides washing in the almost dark is good thinking time.

Let us know how the developing tank works out.

Jason

 

[rwhb12]

More on my emulsion attempt!

In the CP2 I was able to fill the water bath with ice cubes and with occasion pump use to top the water up, the system worked very well. With the nylon bag inside, I was able to turn the bag over the edge of the print drum and noodle into the bag. Iced water and walking back and forth to the bathroom was so much easier.

The CP2 rotation is back and forth, a bit like an automatic washing machine, and appeared to be effective. I had hell of a job getting the lid off, but that is a well known design issue and I will need to make an air pump for my next batch.

scraping the inside of the bag out made a real mess, bits went everywhere. So much waste.

Remelt went ok and finals, with a twist, went in. One grain of thymol out of a new bag, ended with twisters with 20 grains, all went into the final solution. Coating is next.

Ron, I need more light in my darkroom it was the cause of most of my accidents and wastage. I am thinking of purchasing one of the sodium lamp based safelights like a Durst Duka 50 or an multiple range of LED darkroom lamps. Assuming one day we find a panchromatic dye, would these be suitable, or do I have to go IR goggles? The money seems to be about the same.

russ

 

[dwross]

Russ,
You don't need thymol unless you are planning on storing your emulsion for a long time. It's a preservative, not an emulsion ingredient, per se. That is one complication you can remove from the process.

Question: When you say, "assuming one day we find a panchromatic dye..." do you mean one that panchromatizes a colorblind emulsion? That would mean that it sensitizes for more than one part of the spectrum. I haven't heard of a dye that does that (which, of course, does not mean it does not exist). A panchromatic emulsion is a layer cake of sensitivity. It starts with the part of the spectrum native to an AgX emulsion (only slightly different between a chloride and a bromide.) Then you add orthochromatic sensitivity (yellowish green through orangish yellow). The final panchromatic sensitizer(s) adds in red sensitivity. That final one is called the panchromatic sensitizer, even though by itself it would not make an emulsion panchromatic. You may very well know all this, so apologies if it's redundant info for you, but if you do want to read more you can start here: http://www.thelightfarm.com/cgi-bin/htmltutgen.py?content=31Aug2013, going for five pages, with a summary here: http://www.thelightfarm.com/cgi-bin/htmlgen.py?content=24Nov2013

 

[Photo Engineer]

Russ, when you pan sensitize an emulsion, the wisdom is that you not use any safelight at all! None. For ortho, you can use red. For unsensitized you can use either red or yellow.

As for the method of sensitization, you can use 2 dyes and mix the 3 emulsions in one layer. You can use a 3 layer method, but that is uncommon in B&W materials. Or, you can use a panchromatic dye. They do exist and are used in many products to save time and money. One dye, one emulsion, one layer!

PE

 

[falotico]

Do commercial enlarging papers such as Ilford use dyes to sensitize the emulsion to a broader range of visible light? Or is the emulsion made sensitive by chemical means which don't rely on dyes?

The commercial products for enlarging and printing black and white negatives seem to be sensitive to more than just blue light, but this is just my impression.

 

[Photo Engineer]

Multigrade papers are all sensitive to B and G light. They are also sensitive to UV radiation, but then you filter that out of your enlarger illumination.

PE

 

[rwhb12]

Thanks Guys! But I still need to address the safelight question.

I have been reading and researching emulsions ever since leaving GEH and find the whole subject fascinating.

Yesterday, I was reading the BJP from 14jun1912:

"For the professional, fine art and portraiture

Zenith plates at popular prices

The Ilford panchromatic plate is the finest plate - sensitive to all colours that has ever been produced"

the Zenith advertisement changed during 1912, so it is fair to say panchromatic production arrived during 1912. Incidentally none of the other plate advertisers followed. So Ilford had a secret weapon!

The point in rising this is that dyes were limited at that time. I have assembled a crude list. Maybe they were double coating (following Denise's line of thought) in the dark, but their machinery would have been geared up to single coat (in the dark) so what were they using? Maybe they stacked the coated plates, carried them back to the start of the coating machine changed the emulsion, and put them through again? Remember this is 1912, so not a lot of mechanisation and that this was one, new product line, amongst many.

Not sure if this was before Kodak were producing panchromatic plates. Maybe GEH staff might know the answer to this?

 

[pdeeh]

There's a rather lovely book on the history of Ilford called "Silver By The Ton" which gives some details of plate coating at that period, but the index is a little scant ("panchromatic" doesn't appear in it for instance )

I'd probably have to read the whole book again to be sure, but on a quick look this morning, while it mentions the plate machines, says only that panchromatic plates were coated in total darkness (surprise!), but doesn't mention whether it was done in a single pass or two or three. But it does say that pan plates were produced prior to 1912.

 

[dwross]

A misunderstanding (I think) of what I wrote. I didn't mean double-coating, rather a two-step process, involving one emulsion, one coating. Make an orthorchromatic emulsion. That's simply a plain emulsion with an orthochromatic sensitizer added. I use erythrosin, aka Red #3. Then coat and dry as usual. This is all done under red safelight. Then, in the complete dark, take those plates and dip them in a panchromatic sensitizer (I use pinacyanol chloride). Dry the plates (in the dark, of course.) Load them, in the dark, just as you would with commercial film. If the staging is done in the light (either red, or room light if the ortho plates are safely stored in a dark place), the panchromatic sensitizing is a snap. I have complete instructions in the links I posted earlier.

In the old commercial operations, a few years into experience with panchromatic emulsions, and with years of automated or semi-automated factory coating experience behind them, most pan products were made from a single emulsion sensitized for more than one spike in the spectrum. All in complete dark for the most part.

 

[Photo Engineer]

In early coatings made with more than 1 layer, it was common to have multiple coating stations on one machine. I have seen 3 layers being done this way on one machine at EK. So, the plates passed under 3 coating hoppers.

PE

 

[rwhb12]

Thanks for this. Dipping plates in a dye after coating was a popular amateur pastime between the wars but different dyes had a reputation for short lived panchromatic effects. Of course this could have been due to the production methods of the time. Have you experienced this Denise?

This, of course, is just another coating method and not so sophisticated as crystal and dye working in combination.

Russ

 

[Photo Engineer]

Remember that sensitizing dyes are also desensitizers. See the example in my book.

As a result, the dipping method can cause a desensitizing effect if you imbibe too much and as a result you lose overall speed. So, if you use this method, be careful and do a time series.

PE

 

[dwross]

Russ,
I can only speak to one dye -- Pinacyanol chloride. It was by far the most common and considered the best reliable standard of its day. I've never noticed any problems with it. Using the dilution and technique I've spelled out on TLF has given me very satisfying results. Doing your own tests is always recommended.

You can certainly add Pinacyanol chloride to a cooking batch of emulsion -- just as you add erythrosin. But then you'd have to coat and cut (in the case of film) in the dead dark, or maybe with IR goggles. Yuck. Not my idea of a good time, and I do all this for a good time! Dipping plates or sheet film pieces that are all ready to load and use otherwise is a minor effort. But, of course, that is a classic example of 'your mileage may differ'.
d