A simple improvement for MBDCG

Transcription

1 A simple improvement for MBDCG The original formula for MBDCG as invented by Jeff Blyth can be found on this page: [1] This procedure works really well, except that in cold environments often the Methylene blue crystallizes out before the holographic plate can be used. This is likely due to the fact that Methylene Blue (MB) will not stay in a solution with Potassium Chromate when the ph is below 8. In the original formula the ph is prevented from being too high by the addition of Acetic Acid. If the plate is left to dry in a cold environment, the Acetic Acid evaporates more slowly than the water in the plate and the ph drops below this value. A more stable plate can be made with the following procedure: STOCK SOLUTIONS for mixing: TMG: 25ml TMG + 75ml DeIonized water (1,1,3,3-tetramethylguanidine). Potassium Chromate: 4g in 100ml DeIonized water. Methylene Blue: 4g in 1L DeIonized water. Boric Acid: 100g crystals in a bottle. Gelatin: Almost any gelatin with bloom strength of around 220 will do here. Best results are with Bovine Alkaline gelatin, but I have had good results with pig skin gelatin from the supermarket. HOW TO MIX THE STOCK MBDCG SOLUTION: 100ml DeIonized water. Heated to 45C. Add 12g gelatin. Stir until all gelatin is dissolved completely. Optionally, the solution can now be filtered through a fine coffee filter. Add 0.77g of Boric Acid. Crystals until all are dissolved. Now turn on your green safe light. Add 1ml of Potassium Chromate (4% solution) Add 4.8ml of TMG (25% solution in DI water) Check ph of the solution. If too high, add small amount of Boric Acid and check ph again. If too low, add a drop of TMG (25% in DI water) and check ph again. The optimum ph is between 9 and 10. Use an electronic ph meter. They cost about 40 USD. Add 6ml of MB (0.4% in DI water). A SIMPLE WAY TO COAT YOUR PLATES WITH AN EXTREMELY FLAT COATING IS AS FOLLOWS (MOLD COATING): Clean two glass plates with normal dish washing detergent (for hand wash). Clean both plates with Glassex (Windex in USA), or other Ammonia based window cleaner. Treat one glass plate with Rain-X to make it water repellent. Stick Scotch tape to two opposite sides on the other glass plate. Heat both glass plates with a hair drier. Put a small amount of stock MBDCG on the Rain-X treated glass plate and gently lower the other plate (the one with the Scotch Tape on the two edges) on top of it.

2 Allow this sandwich to rest for about two hours. After two hours the plates can be separated by holding them vertically and gently wedging a sharp knife in between them. If all went well, the glass plate that was not treated with Rain-X will now have a perfectly flat coating left on it. Leave this plate to dry for a few hours. After that it is ready to by cut to smaller pieces and to be used. OTHER WAYS TO COAT: A Coating Rod can be used (Meyer Bar). This requires some practice. Both the plate and the coating rod need to be heated. It is essential that the coating rod is drawn over the plate at a very constant speed. The Victorian Curtain methot. Hold a pre-heated and cleaned plate at an angle and pour the MBDCG solution along the edges and along the top. Steeper angles make thinner coatings. This method works well, but the top of the plate will have a thinner coating than the bottom. MBDCG is very sensitive to variations in thickness of the coatings. If this becomes a problem, try the above method (Mold Coating). HOW TO USE THE PLATES: The plates can be exposed just like any other holographic plate. They are somewhat less sensitive than silver halide plates though. They need about 30mJ per square centimeter. Thicker coatings are less sensitive due to the fact that they are less transparent. Perhaps using less MB in thick coatings will compensate for this. After holographic exposure, the following counter intuitive trick will greatly improve your hologram: during a period of one seventh of your exposure time, expose the plate in diffuse laser light (ie just wobble the plate in your expanded laser beam). This will greatly reduce noise in your hologram. Also, the hologram will be less sensitive to variations in processing temperature. Next, process as follows: Leave the plate several minutes in a tray with water. Do this until all MB has dissolved out. The lights may be turned on now as the plate has lost it's sensitivity. It is a good idea to give the plate an additional rinse under cold running water now to ensure removal of the last traces of TMG from the emulsion as TMG can contaminate the subsequent alcohol baths and reduce their effectiveness. Dip the plate in a tray with warm water, about 30 seconds. First try a temperature of 25C. More about this later. Very quickly transfer the plate in a bath of 70% Isopropylalcohol and 30% water. Leave it in there about two minutes. This must be done in one smooth and fast movement because no water is allowed to dry or flow off the plate in between the water bath and the first alcohol bath. Dip the plate in a bath of 100% Isopropylalcohol. (about two minutes) Dip the plate in a second bath of 100% Isopropylalcohol. (about two minutes) Put the plate on a dry towel (emulsion up), and dry it with a hair dryer set to HOT. If all went well, you will see an image slowly appear. If you see some crystalline structures appear on the

3 plate, continue to blow dry. They will disappear again. (This is an indication that the optimum temperature for step 2 has been reached.) If the hologram looks blue or dark green and is very dim, it can be re-processed. Starting at step 2. But this time at a slightly higher temperature. The hologram will come out brighter this time. At a certain temperature, the hologram will finish at a very pretty golden colour. It will be broadband now and not have so much depth. If processed at a higher temperature than the one that results in the golden colour, the hologram will be noisy and milky. Low temperatures in step 2 make very sharp narrow band holograms. Higher temperatures make less sharp broad-band holograms. THINGS THAT CAN GO WRONG: Be careful with chemicals and read the relevant MSDS (Material Safety Data Sheets) each time before using. If there are random variations in brightness across the processed plate, it has not stabilized to the ambient humidity yet, or it has not dried long enough. Drying can be accellerated with a hair drier set to cool. This can cause some dust to adhere to the plate though. If the gelatin detaches from the glass plate during processing (usually happens during the washing bath in step 1), don't be tempted to take it out of this bath before all the MB has washed out. Putting a plate in Isopropylalcohol that is not clean, will contaminate this bath and make it useless. If you only use clean plates in the alcohol baths, these baths can be used many times. Detachment can be prevented with an extra pre-processing step during the cleaning of the glass plate as follows: Make the following mix: 40ml 3-aminopropyltriethoxysilane + 45ml IsopropylAlcohol + 5ml DeIonized water. After 24 hours, take 1ml of this stock solution and add 20ml IsopropylAlcohol. Rub a cleaned glass plate with this solution. A white haze will appear across the glass. Leave the plate for about two hours and clean again with Glassex (Windex in USA). The glass is now sticky to gelatin forever. Gelatin will not detach anymore from this glass. Mark the glass with a small dot of a black waterproof CD marker so you can tell the difference between a silanated glass and a Rain-X treated glass. Plate is insensitive/very dark blue before exposure and takes more than 5 minutes to become transparent in the washing bath. This happens when the coating is too thick. Try a lower concentration of gelatin or less Methylene Blue in the stock solution. There is foam on the gelatin solution before coating it on the glass. This results in ugly tiny air bubbles in the coating. Allow the MBDCG stock solution to cool and gell before using. When it has gelled, the bubbles are on top of the gelatin. They can now be cut out with a small plastic spoon. Random colorations appear across the plate. This happens when you don't transfer the plate from the warm water bath quickly enough into the first alcohol bath. Try to cover the gelatin side with a cover glass or plastic sheet (while in the warm water bath) before moving it into the alcohol bath. Once fully submerged in the alcohol bath, remove the cover. Random spots of Pretty Golden Area's appear across the plate (usually at the sides of the plate): Hah, you have found the threshold temperature in your warm water bath, above which the hologram becomes a golden colour. Re-process with the warm water bath one degree Celsius higher. USEFUL TIPS: A great way to measure small amounts of liquids is to use a 10ml syringe. Use the type with rubber seals because they operate more smoothly. A great way to measure small amounts of solids is to use a digital scale used to measure the

4 weight of letters. Make sure that they have a resolution of one gram or less. Stock solution stays usable a very long time. Do not allow it to freeze though. I haev re-used stock MBDCG six months after first mixing it. Plates stay usable a very long time. I have exposed a plate that was two weeks old with no difference in sensitivity. Unlike silver halide plates, MBDCG plates are very resistant against accidental exposure to light. In fact, I keep my ready-made plates in my house. Before exposure I quickly walk with them in broad-daylight to my garage and use them. Use a green light as a safe light. Don't worry if there is a small amount of red left in your safe light. MBDCG is not sensitive enough to be problematic with small amounts of red light. You can check the spectrum of your safe light by looking at it's reflection in a dvd. If you see only green, perfect!!! If you see some red, no big deal for MBDCG. Unlike silver halide plates, MBDCG plates are very VERY SUPER resistant against accidental exposure to light. I think this is because of non-linear behaviour of the plates. I once tried to expose a plate that had been in my house uncovered for two days. Sure enough, a dim hologram could be made with it. :) Don't be satisfied with a dim hologram. MBDCG holograms can be very bright. So bright in fact that you don't have to paint them black on the back side. You will not be able to see through a good MBDCG hologram when it is properly illuminated. MBDCG holograms are somewhat sensitive to moisture. If you want to keep your hologram in good condition a long time, it has to be covered with a protective glass plate and sealed on the sides. If you don't do this, the plate will fade over time. The good news is though that you can re-process the plate. It will look as pretty again as when you processed it the first time. Stock MBDCG solutions last virutally forever. You need about 2 ml to cover a 10x15cm plate. So you can make about 50 plates from 100ml of stock. You can make about a liter of stock MBDCG from the pre-mixing solutions above. A 10x15cm plate needs about 3 minutes of exposure time at 50mW. And about 25 seconds of diffuse post exposure to harden the plate. If you are in a real big hurry to mix MBDCG stock and don't worry about small lumps in the solution, the following procedure works well (I have never seen the small lumps, but some people have had them with certain types of gelatin): -100ml DeIonized Water -4.8ml TMG -Add small amounts of Boric Acid crystals until the ph drops to about 10. (about 0.77 gram total). -1ml Potassium Chromate (4%solution in DI water) -6ml Methylene Blue (Diluted to 0.4% in DI water) -Add 10g gelatin. -Check ph again. This has the added advantage that the gelatin dissolves much faster due to the higher ph and no air bubbles form in the solution.

5 If you store your plates in another location than the one where you expose them, they need some time to adjust to the temperature and humidity of the location where you expose. A quick way to adjust the plate is to blow it with a hair drier set to COLD for a few minutes. You don't need a magnetic stirrer to mix MBDCG. Simply use a cheap hot plate. Put a pan with sufficient water on the hot plate and set the plate to a temperature of about 40C. Then place the glass container in which you mix the chemicals in the pan. The water in the pan now functions as a temperature buffer and will react more slowly to too high or too low settings of the hot plate. This also has the added benefit that ph meter and plastic spoons can be cleaned in the water that is in the pan. Don't allow the temperature to go over 50C. Use plastic trowaway spoons for mixing and measuring chemicals. That way you (or your better half) will never make the mistake of putting them in the dishwasher or with the spoons that you use for eating. Clearly mark all glassware and pots and pans that you use for MBDCG with a scary looking skull and write poisonous on them. Then store them in a place where children cannot touch. Instruct family that ARE qualified and able to be close to the chemicals and equipment: If anything falls over or is noticed to be leaking... WALK AWAY AND CLOSE THE DOOR!!! Then tell you what happened. Tips from Cristiano Perrucci: I would like to emphasize this method requires a few little adjustements: MB concentration SHOULD be tuned for optimum results depending of gelatine hardness and tape you are using (mine is 3.1 mils) Gelatine concentration MUST be tuned for differents kinds of gelatine and TMG concentration. During gelatine pouring, glass plates SHOULD be controlled for better results, and kept closely to emulsion temp. Traces of water repellent (I'm using Rain Clear as Rain X is unknown here in Italy) on glass surface helps to get a really smooth coating. SO-DCG for Green Lasers You can substitute MB with Safranine "O" and shoot with a 532nm laser and keep everything including concentrations just the same as with MBDCG). Safranine "O" is fully compatible with MB so you can do 2 colour ones. Exposures are the same as G307, however G307 can not be made panchromatic.