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Information: http://www.holoworld.com/ also
http://www.holografie.com/ld01.html
Make your own material: http://www.holoworld.com/holo/worksheet.html
Before exposure, plates greatly benefit from a presoak for 30 sec in 7% TEA (Triethanolamine) under safelight. Followed by squeegeeing off excess with a windscreen wiper blade. This can increase their photosensivity considerably. If you leave the TEA in the emulsion and dry the plate in air before exposing , you must allow at least 30 minutes (preferably even more) to allow plate to stabilize and stop “creeping” after this treatment. TEA treatment gives the brightest results and shifts the replay wavelength from red to yellow/green if it is not washed out. Even if you don’t want your plates pre-swollen because you want your picture to be orange-red , you still gain in photosensitivity after you wash out the TEA before exposing.
A good developer for both transmission and reflection holograms is :
Water (distilled or deionised) …700 cc, Ascorbic acid-(Vitamin C)…25g ,
Sodium carbonate anhydrous…50g,
Sodium hydroxide… 20g,
Metol …4g . Make up to 1 litre
This should be used in a plastic dish with an identical dish floating on the top so that there is a minimal air gap. If you use it like this the same developer can be used again and again for many days otherwise this developer left in an open dish is more vulnerable to oxidation from the air than standard developers because it does not contain sulfite ions.. So the time the developer spends exposed to the air is low when you use a floating dish and it is only while immersing your plates or taking them out that it is fully open to the air.
The exposure time should be sufficient to enable the developer to get enough density in under a minute (optical density in centre should be around 2.0, see below).
DON’T BE TOO TIMID ABOUT SAFELIGHTING.
It is important to see what you are doing and how things are developing even if a small amount of fogging may be occurring. A little bit of fogging is OK if you are going to bleach your holograms. For red sensitive plates I use a 10 or 15 watt green bulb as safelight about 10 ft away, (usually a bit of black tape is preferable around the join between the glass and the metal base to stop white light leaking through.
.
How much development time?.- A test method: Leave a small piece of plate in very bright light for a while and then leave it in developer for 5 mins. so that it goes as dark as possible. Rinse and dry it. Now when you develop your holograms under safelight you should use this dark piece of plate to look through at the safe light (it will still have some transparency). You then know that your holograms must never go as dense as that or you have gone too far on developing. .It is OK as a working principle to take your plates to no more than half that density in their darkest areas by looking through at the safelight filament with one eye shut. (Plates continue to develop well in air without staying in the dev. bath all the time.)
After developing, plates are rinsed under tap and dropped into the following bleach bath.
After about 20 seconds the bleach progress can be viewed under white light.
Bleaching
A simple successful bleach is:
Copper sulfate crystals (Blue) …………….35g
Potassium Bromide …………………………70 g
20g Sodium hydrogen sulfate crystals( or 20cc acetic acid)
Dissolved up in 1litre.water (tap water is OK here).
In this bath the black silver disappears rapidly and you can then rinse under tap.
The reflection hologram (if you have one) will appear only when the plate is dry.
Queries : jeff@biotech.cam.ac.uk or
tel:01223 334152
I have devised a remarkably easy way (compared to what was known as the
conventional method) to make recording material.
A worksheet (dated Nov 2000) is given below. It gives results which have
good diffraction efficiency and photosensitivity compared to ultrafine grain
proprietary material. But this is for the fun of doing it all yourself and
getting bright results. If you are particularly concerned about marks from bubbles, dust and blemishes then
you may prefer to use the proprietary
material.
A simple way to make silver
halide hologram recording plates by
Diffusion
By Jeff Blyth, Institute of
Biotechnology , University
of Cambridge Tennis court rd. Cambridge CB2
1QT
Tel : 01223 334152 ( fax: 334162 ) email : jeff@biotech.cam.ac.uk
What follows is in the form of a worksheet based on the paper published in :
The Imaging Science Journal Vol 47 pp 87- 91 1999
[A text only
version of the paper can be found on the internet on the websites:-
http://www.holoworld.com/holo/paper.html
or at:-
http://www.holografie.com/paper.html ]
The Basic
principle
A coating of pure gelatin on a glass plate is treated with silver nitrate. The coating is then immersed in a bath of bromide ion and dye. This then precipitates extremely fine grains of silver bromide in the gelatin layer.
Materials
1)Presubbed glass plates . (You can use old holographic plates with the gelatin removed with the aid of household bleach.)
2).Gelatin of “bloom strength” between 250 and 300 (eg. 300bloom from Aldrich cat no. 27,162-4) , (You can use culinary gelatin without any sugar or flavourings.)
CHEMICALS (All available from the Aldrich Chemicals).
( 3)ascorbic acid or Vitamin C,
4) Silver-nitrate , (A 1N volumetric standard solution is a useful form)
5) Potassium Bromide
6) Chromium acetate , (you can use “chrome alum” instead)
7) dye(s): Pinacyanol Chloride (for HeNe 633nm exposure) or
1,1 ‘-diethyl -2,2’ cyanine iodide for exposure at 532nm .
8)Sodium hydroxide
9) (for new glass plates) 3-amino-propyltriethoxysilane
Concentration of
Solutions (quantities will need to be judged by you to suit your
requirements)
Silver nitrate : 6%
w/v in (DI) water , (or the “ 1N volumetric standard solution”
diluted by 1volume to 2 volumes DI
water.)
Stock dye solns : for 633nm 1g. /1000 ml Methanol, but for 532 nm dye, 1g. per 500 ml methanol .
( In practice you would probably only need a hundreth of a gram to make up a few ml of these somewhat expensive dyes.)
Potassium bromide 4% w/v in 50/50 methanol /water
Chromium acetate solution 1% or Chrome Alum 2%
Gelatin solution. 15%: (see 2 paragraphs down)
Ascorbic acid 1% solution in water , adjusted to around pH 5 with any alkali.
Preparation of plates . Glass plates usually need a pre-treatment step or
the gelatin coating will peal off. You can use old holographic plates by simply
giving them a 10 min. soak in neat domestic bleach solution and then rub off the old gelatin layer under
tap water. After a final rinse in distilled water, no further subbing step may be required.
However
with new glass plates, I leave them soaking overnight in a 100% bleach (“Domestos or “Parazone”). After the plates
are dry I rub them over with a 2%
solution of
3-amino-propyltriethoxysilane in
acetone on a tissue until it has evaporated, and leave them in air to interact
with the silane for at least two hours
before coating. (The silane solution has to be freshly prepared for each batch
of plates).
Preparation of coating
solution for a 10’’ x 8 “ plate
Add 30g gelatin to 170ml cold (distilled or deionized) water and mark the liquid level on the beaker. Place beaker in a water bath and heat while stirring constantly until gelatin solution is between 70 and 80o C.
Stir until all granules have cleared. Top up level to the
mark . To remove skin and surface foam,
pour through a fine mesh (nylon stocking works fine) into a preheated
beaker. Then immediately proceed to
next step:
Coating( by the old
Victorian curtain method)
Hold the beaker in your right hand and with you left incline the presubbed glass plate (preheated to around 70oC) at an angle of about 30o to the vertical with its bottom edge in a clean tray. Pour the gelatin in a line about 1 cm from the top of the plate. The pouring rate must be continuous until the furthest edge of the plate is reached . (You may have to accept the tendency of the coating to not completely cover the lower part closest to the furthest edge. ) Lean plate against something for a few minutes while coating gels. Run a knife along thick layer at the bottom to free plate rather than risk tearing the delicate coating. (Since no hardener is involved yet the gel can be readily scooped up and recoated if you are not satisfied.). Put plate in cold solution of chromium acetate for 1 minute. Shake off drips and then (without washing away that salt ) blow plate with cold air until dry. Once the layer is dry leave the plate to complete the chrome hardening effect overnight in a warmer. (Preferably at around 60oC for several hours). Rinse the hardened plate in DI water and dry in a warm air flow. If you want to cut plate up for the next step then after scoring the glass on the back and cracking it, it is best not to pull sections apart before running a scalpel blade along the gelatin side first so that it is cut and not torn apart..
Alternatively a
“Meyer bar” can be used. About 7
turns per cm.
AgBr loading
operation.
1. For a 5 x 4” plate place approx 3 ml 6% silver nitrate soln. in the centre and at once squash it with a clean flat cover plate (preferably transparent plastic so that you can see the air bubbles are squeezed out). Leave for 3 minutes. Safelighting is not strictly necessary here but white lighting should be subdued.
2. Remove cover plate and immediately remove the excess silver solution on its surface by gently brushing over the plate with a soft squeegee (windscreen wiper blade).
3. Blow dry plate with cool air.
5. Under safelight conditions , add 2.5 ml of dye solution per 100ml of lithium bromide solution , add about 0.5 ml of 1% ascorbic acid solution (this is the same solution as is used in the final sensitizing bath ) agitate the bath and plunge plate in while maintaining the agitation for about 4 minutes.
6. Rinse well under running tap water (any AgBr only on the surface can be removed
by gently rubbing with ungloved finger.) Plates usually come out this bath beautifully clear under the green safe light, without any surface deposit.
7) Sensitizing bath step
The plate can be immersed for 1 minute in 1% ascorbic acid solution adjusted to pH 5 using a little sodium carbonate or hydroxide . Alternatively the well known triethanolamine pre-swelling technique can be used with the advantage of increased brightness at a shorter wavelength. (prolonged settling period may then be necessary however to avoid creep while the exposure is being made).
After exposure the plate is then developed as per the first part above.
Queries: jeff@biotech.cam.ac.uk or Tel. 01223 334152