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That's an excellent reading the Simon Brown‘s . I think this film is made onto a polyester support due the long roll characteristic and the fact that it need to be kiss cut, not mention the ISO water process.

It is a good source for cheap Halide films but not more practical for any commercial use.. Mastering is was the key start point in industry, both embossed or volume photopolymer. For long time embossed give away SH using lasers, but SH is still necessary for some niches.

EDTA-based elements are quite difficult to obtain in France due to regulations, is there an honorable substitute you might know about ?

I need to bleach these "HoloFilm 250 PAR"

thycore wrote:EDTA-based elements are quite difficult to obtain in France due to regulations, is there an honorable substitute you might know about ?

You should be able to get EDTA (mostly NaEDTA though) through sites related to alternative photography. Take a look e.g. at. http://disactis.com/store/fr/21-chimie-gnrale

Is NaEDTA equivalent to Ferric EDTA for our holographic bleaching purpose ? or do I have to somehow "break" NaEDTA and mix it to cook my own Ferric EDTA ?

No the EDTA just acts as a moderator to the iron bit which is in a Fe+++ state. Each + means a missing electron from the iron atom .This iron ion wants to grab back just one electron from somewhere. So when it encounters the developed up dark silver metal atom that metal has one very removable electron whizzing around its outer layer. Therefore the Fe+++ ion grabs it and becomes Fe++ and the Ag metal changes from being an uncharged atom to being a charged ion Ag+. The many other electrons whizzing around the Ag ion are not up for grabs so it stays as a single charged ion. Also the Fe++ ion is quite satisfied with having taken just the one electron and has no appetite to take any more, ( in fact if you tried to give it any more to turn it into iron metal it would be quite a strong chemical reaction struggle). In the early days of holography a bleach advocated by Nick Phillips was Ferric Nitrate and that became commonly used in the 1970's.
However it was only stable as a very acidic solution. This had some detrimental effect on the gelatin. By adding a sodium salt of EDTA , it was found the ferric ion could stay stably in solution up to a almost neutral pH .[ pH6 instead of about pH 0 ], and yet it could still bleach the Ag metal without damaging the gelatin. EDTA is a strong complexing agent for the iron ions. The EDTA stands for EthyleneDiamine Tetraacetic Acid; that means the ideal compound (sold by Sigma-Aldrich cat no. 162101-36-2) has the 3 positive charges on Fe+++ bonded to 3 negatively charged acetic acid bits with the 4th acetic acid bit attached to a single sodium Na+. I find that gives the best diffraction efficiency bleach for Denisyuk holograms, even better than using copper salts. Eg. 40g Ferric EDTA (Aldrich) , 60g. potassium bromide,and 70 ml acetic acid made up to 1 litre.

Good to "see" you here again, Jeff!

For people not having access to Aldrich, the common route would probably be to get ferric nitrate/ ferric sulfate and sodium EDTA.
Regarding Na EDTA I noticed that most alternative photography supply shops rather sell trisodium than disodium EDTA.
I believe to have used either form in the past to make ferric EDTA bleaches.
So I assume trisodium EDTA simply requires a bit more acid (acetic acid in your formula). Is that correct?

Yes that is right Martin. Basically you need just one molecule of EDTA per molecule of “ferric ion”. It does not matter in my formula if the EDTA has its acetic acid groups combined with 0,1,2,3 or 4 sodiums because I use a large excess of acetic acid which would swamp any differences. But there is the problem that those sodium salts contain varying quantities of water when you buy them so you don’t know the actual amount of EDTA you have got to match up with the ferric ions. Aldrich only lists the anhydrous molecular weights even though their salts are hydrated. The free unsubstituted acid is water-free however. If you cannot purchase the correct salt from Aldrich with its correct ratio of EDTA to Ferric iron then I guess you could get the ratio about right by using pH as a guide. So if you add say about 20 grams of your tri-sodium EDTA salt to say 800 litres of water ,then as you stir in your source of ferric ions from Ferric sulphate or nitrate the pH would stay up above 7 until you reach the point where it would suddenly drop because the ferric ions are in excess. Incidentally one should not use the easily available ferric chloride[printed circuit board etchant] as ones ferric source because high levels of chloride ions in the bleach can cause grain growth and scatter.

PS I meant 800mls of water, not litres

I finally managed to prepare the D-19 based on the initial formula, I made 500mL instead of 1L, so I divided all quantities by 2 :

2 g Metol
90 g Sodium Sulfite
8 g Hydroquinone
52.5 g Sodium Carbonate (monohydrated)
5 g Potassium Bromide
One litre water

I labelled a bottle D-19 with today's date as a reminder of the approximate lasting period of 6 months if correctly tapped from air.

The preparation is perfectly clear & uncolored (I hope this is how it's supposed to be I prepared my film holder (2 x 25cm square 4mm width glass panels held in place with 2 wooden frames with 4 strong screws, i'll put the Holofilm 250 sandwiched within).

I ordered the Bleach chemistry elements on eBay to bypass usual FR regulations, and waiting to cook it before I make a first test with this new film.

My subject will be a nice little Astrolab : Thank you all so much for your precious experience feedback & advice

Thank you for the important info, Jeff.
Remains to emphasize once more the outstanding keeping properties of the ferric EDTA bleach.
My EDTA bleaching solution is about 25 years old and still working…