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Recipe: 'AmBr' with Variations

September 7, 2013

Developed by Denise Ross for The Light Farm, 2013.

The techniques for making the basic recipe are covered in previous tutorials. The information in this recipe builds on the experience you have had up to now. It is not written for a first-time emulsion maker. This is also true for most recipes in the historical literature. Once you start making emulsions, you will recognize that the old recipes aren't nearly as mysterious or misleading as is sometimes suggested — often by people you would think should know better. Their issues may hinge on the fact that the home darkroom is not a factory and artists don't have to be engineers. But, artists do need to follow good practices. Work safe. Work smart and consistently. Take excellent notes. Have fun.

The basic recipe is divided into three steps. They can be completed one after another on the same day, or divided into separate work sessions up to a week apart, according to time available. The steps are Precipitation, Washing, and Ripening & Coating. In addition to the three main emulsion making steps, time must be allocated for glass plate blank preparation, and for drying the coated materials. Drying plates or film can take more than a day if the weather is humid. Cutting film adds an extra step, as does panchromatic sensitizing.

To the list of ingredients we have used so far, add erythrosin B (a.k.a. "erythrosine") for ortho emulsions, and erythrosin and pinacyanol chloride ('PinCl') for panchromatic emulsions, and Yellow #5 food dye if you want to add self-screening to either emulsion.

In addition, I dissolved my PinCl in methanol. That was recommended by the service rep at Lab Depot. It is also soluble in water and in ethanol. What a dye is dissolved in may change its sensitizing range, but that is not something I have pursued yet, and I'm not sure I will — or at least not soon. It is, though, a worthy question to answer.

You need a 1% PinCl solution. That is 1g in 100 ml of solvent, or 250 mg in 25 ml solvent. Since there are 20 drops in a ml and you will only use 1-2 drops per sensitizing session, 25 ml of prepared dye will last a long time. Store the prepared dye in a dark amber glass dropper bottle. In turn, keep the dropper bottle in a black plastic bag (or other lightproof container) in the refrigerator. It is supposed to keep indefinitely this way. I don't know whether or not the solvent used influences its useable lifespan.

The erythrosin solution is made to 2% and you will be using more of it. I would buy 1 g and mix it with 50 ml of solvent. It is dissolved in a solution of half distilled water and half ethanol. I use Everclear drinking alcohol. Lab and shop grade ethanol have added ingredients and I have no idea whether or not they might affect the solution.

Making the dye solutions is very easy, but does require attention to prevent getting any dye dust into the air. Both powders are amazingly concentrated. Buy the exact amount you want to mix up and avoid the inevitable disaster of trying to weigh out the stuff.

Have ready and lined up: your bottle of dye, an amber dropper bottle of appropriate size (impeccably clean, of course), a clean glass beaker (about 2x the volume of your final solution), a clean plastic spoon, and your measured-out solvent in a beaker or graduate that pours cleanly. Wear latex or nitrile gloves. Never get your face near the materials as you are preparing the solutions. Wearing a basic dust mask is optional, but prudent.

Carefully open the bottle of dye powder. Add some solvent about half way up the bottle. Carefully swish it around in the bottle. Pour the solution into the beaker. Add a little more solvent to the dye bottle and repeat. Slowly stir the contents of the beaker as you add the remaining solvent — except for a little that you hold back. Pour the dye solution into the amber dropper bottle. Pour the remaining solvent into the beaker, swish it to get most of the last of the dye solution clinging to the beaker, and then pour that into the amber bottle. Wipe out the beaker with a paper towel before you clean it with soap and water. Label the dropper bottle, including the date prepared, the concentration, and the solvent used.

Note: This recipe doubles well. The resulting ball of refrigerated, pre-washed emulsion still fits in a standard potato ricer. The single recipe presented here coats twelve to fourteen 4x5 (inch) plates.

Step One: PRECIPITATION

Pre-heat a 55°C waterbath.

Salted Gelatin: In a 1-cup Pyrex measuring cup or 250 ml beaker, thoroughly dissolve together:

  • Distilled water ..... 45 ml (45 g)
  • Ammonium bromide (NH4Br) ..... 4.1 g

Add:

  • Gelatin ..... 2 g

Cover, bloom 15 minutes, and then place in the waterbath. Let sit 30 minutes, making sure the waterbath temperature comes back to 55°C. Stir in:

  • 10 % Potassium iodide solution (KI) ..... 1 ml (20 drops)

If you are making either an ortho or panchromatic emulsion add:

  • 2 % erythrosin solution ..... (3-4 drops)

While the Salted Gelatin is melting and coming up to temperature prepare the Second Gelatin and the Silver Solution.

Second Gelatin: Mix together, cover, and set aside:

  • Distilled water ..... 25 ml (25 g)
  • Gelatin ..... 5 g

Silver Solution: Dissolve together:

  • Distilled water ..... 45 ml (45 g)
  • Silver nitrate ..... 5 g

Right before precipitation, temper (warm) the silver solution in a very hot small waterbath.

CAUTION: At all times when handling silver nitrate, be very careful. Silver nitrate is a powerful oxidizer and stains anything organic it comes in contact with. If you get stains on your skin they cannot be washed off. They will be part of your skin for weeks. If you get silver nitrate in your eyes, the damage could be blinding. Don't be afraid, just be careful. Silver nitrate is no more hazardous than many common household cleaning chemicals. Bleach and drain cleaner come readily to mind. On a happier note, there are no hazardous fumes involved with a plain silver nitrate solution.

  • Set a timer for 10 minutes.
  • GO TO SAFELIGHT.
  • With constant, consistent stirring, add the silver solution to the salted gelatin at a rate of 1 teaspoon (5 ml) every minute until the solution is gone.
  • Stir until the end of the 10 minutes.
  • Let the emulsion sit in the waterbath, without stirring, for an additional 10 minutes.
  • If you are using a magnetic stirring bar, remove it with a plastic fork.
  • Add the second gelatin. Stir in thoroughly.
  • Pour the emulsion into a ziploc-style plastic sandwich bag, seal, and place in a cold, lightproof container.
  • Cover to exclude all light and refrigerate for a few hours to a few days.

Step Two: WASHING

Have ready two thermos containers — one for washing and one for holding ice water, a potato ricer (or noodler of your choice), washing bag, a small rubber scraper, and the lightproof container (still covered) of emulsion, plus a supply of water if you aren't doing this next to running water. Almost fill the washing thermos with ice water. Position the washing bag over the mouth of the thermos. Set the bowl of the ricer in the bag and ice water. Note: No matter how you are noodling, the idea is to do it into the ice water so that the shreds stay cold and separated.

  • Set a timer for three minutes.
  • GO TO SAFELIGHT.
  • Open the container with the plastic bag of emulsion. The emulsion will be a cold, rubbery ball. Pull out the ball (in one piece or several) and put it in the potato ricer. Press the emulsion through the ricer into the ice water.
  • Scrape all of the emulsion clinging to the ricer into the washing bag.
  • Tie up the washing bag tightly, and dunk it up and down in the ice water for five minutes.
  • Take the bag out of the ice water and give it a gentle squeeze.
  • Pour out the ice water and replace it with fresh. You can catch the pieces of ice in a colander and reuse them.
  • Repeat five times for a total of six (30 minutes washing).
  • After the last washing take the bag (which will be about doubled in weight) and squeeze it in the ricer. Squeeze firmly (but not hard enough to burst the bag!) Squeeze until little-to-no water is coming off. Pat dry with a clean towel.
  • Dry out the lightproof container and place the washing bag in it. Cover securely and refrigerate until it's time to ripen and coat. You can do this immediately if you are ready to go. The time the emulsion is hardening in the refrigerator is plenty of time to stage coating. Or, you can refrigerate the shreds up to several days. Note: Never freeze emulsion at any stage.

Step Three: RIPENING & COATING

Have your plates ready for coating and a pre-heated 55°C waterbath.

GO TO SAFELIGHT.

  • Scrape the noodles out of the jelly bag into a 400-500 ml / ~2 cup container that fits with your waterbath.
  • Stir in 1 teaspoon (5 ml) Everclear mixed with (optionally) 2 drops 10% KBr. The KBr is added insurance against excessive base fog.
  • Set the noodles in the waterbath for 60 minutes. Don't stir. Alternatively, you can stick a thermometer in the emulsion and pull it out of the waterbath when the temperature reaches 55°C.

  • Take the container of emulsion out of the waterbath and set it in a bowl of cool water so that the water comes up to about the level of the emulsion.
  • Very slowly and gently stir the emulsion with a plastic spoon until the temperature reaches 34-35°C.
  • Very gently stir in 5 ml Everclear (and, if adding self-screening, mixed with 2-5 drops, or more depending on your needs, Yellow #5 food dye.)
  • Coat with the emulsion in the low-to-mid 30s°C. This is never a hard and fast number. It is influenced by whether you are coating glass or film, and their temperature when you coat.

Panchromatic Sensitizing

EDIT NOTE, 1/26/14:
I've been refining the panchromatic sensitizing process hopefully to make it easier and more consistent. Please go here for the details.

Panchromatic negatives are orthochromatic emulsions with additional red sensitivity. Therefore, you start with ortho plates or film.

You will need two tray-type containers. I strongly advocate getting brand new plastic food containers and using them only for sensitizing. Cross contamination is not our friend. Have one a bit larger than your material, and a second a bit larger than that. Freeze an inch of water in the bottom of the larger tray.

In preparation, on your coating table, spread out a clean towel big enough to hold all your plates or film sheets when they are drying flat (or slightly bowed in the case of film. I haven't tried hanging film while the sensitizer is drying).

Up until now, whether colorblind or ortho, you could work under a red safelight. When you sensitize panchromatic you must work in the dark, or use a very dim headlamp. Fortunately, all prep work right up to the actual sensitization bath can be done by regular safelight. Start with having your materials in the form that you will use them to shoot, i.e. plates separated, and/or film cut to size. From now until fixing is complete, you must work in the dark or by headlamp.

When it is time to sensitize, in the smaller plastic container add 1% pinacyanol chloride solution to cold distilled water. I have been using 2 drops in 300 ml cold water for 4x5 inch plates and sheet film. Mix thoroughly with a clean plastic spoon. Set the container with the dye water on the ice in the larger container. Working cold prevents the emulsion from softening during sensitizing.

Slip a plate or piece of sheet film under the surface of the bath. Gently rock the container a couple of times. Let it sit in the bath for 5 minutes with a gentle rock once a minute. Then, lift it out and set it on the drying towel. Repeat with the rest of your materials. Let everything dry completely before storage or use. (Note: A 5 min. bath is what I've been using sucessfully, but time in the bath may be a sensitizing variable worth exploring.)

TIP: I have only recently hit on a great trick for handling plates with minimum damage to their edges. I use a hard plastic small spatula (pancake turner). It slips right under the plate. A slight lift of the plate with the spatula lets me get my fingers under the plate to safely move it from place to place without having to touch the edges.

The tutorials will return next spring.
"editor at thelightfarm dot com"

Denise Ross



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