Dehydrating with methanol instead of IPA?

Dichromated Gelatin.
pluto
Posts: 95
Joined: Fri Feb 05, 2016 2:06 am

Dehydrating with methanol instead of IPA?

Post by pluto » Fri Dec 15, 2017 1:40 pm

Isopropyl alcohol is obscenely expensive here in Canada, about $6 or $7 for 500mL.

Methanol (often labelled "99.9% pure Methyl Hydrate") is quite cheap however! It can reliably be found for $10/4L and often much less. An equivalent volume of IPA would cost over $50!

Since the primary function of the IPA is to dehydrate the emulsion, it should be OK to substitute it with methanol, right?

I'll try to determine the effectiveness of methanol by using it to develop a hologram as if it were IPA, observing the hologram, then doing an IPA wash and observing the hologram again. If the hologram doesn't improve from the IPA wash, I think we can be sure that methanol is just as good :)

I will report back with my findings, but it would be great if somebody here could test it out as well. I'm just returning to holography after a year hiatus, and was never particularly good at it in the first place, so it would be good if somebody else could try this as well. If it works then we can all save a little bit of cash :)

Thanks!

P.S. What are your local prices for IPA and methanol?
Last edited by pluto on Sat Dec 16, 2017 10:04 pm, edited 1 time in total.

Sergio
Posts: 96
Joined: Tue Jan 20, 2015 12:25 pm

Re: Dehydrating with methanol instead of IPA?

Post by Sergio » Sat Dec 16, 2017 8:37 pm

I think it will work.

The dehydratation is faster however.

Here right on South America, Brazil is $8/5 L methanol, IPA 10 times more expensive, coincidence?

jeff-blyth
Posts: 20
Joined: Sat Feb 18, 2017 9:41 am

Re: Dehydrating with methanol instead of IPA?

Post by jeff-blyth » Thu Dec 21, 2017 5:41 pm

I did try this once and concluded that it did not work nearly as well as ipa. The problem being I think, that gelatin has a slight tolerance to absorbing methanol, therefore methanol cannot rip the water out of gelatin as well as ipa can. However that really only applies to the final bath. I bet you could use a cheap grade of methanol (which is probably already ~ 5% water?) as an initial bath and only use ipa for the final bath. Acetone has been successfully used until it unfortunately caused
a serious fire if my memory is right.

pluto
Posts: 95
Joined: Fri Feb 05, 2016 2:06 am

Re: Dehydrating with methanol instead of IPA?

Post by pluto » Fri Dec 29, 2017 4:26 am

That's too bad about the methanol -- I still haven't tried it myself, but will do next time I'm developing.

Acetone is about half the price of IPA where I live, but like you mentioned, it's extremely volatile and quite a fire hazard. Also dissolves some plastics.

I'm thinking that maybe a mixture of IPA and methanol might work. The idea being that IPA can penetrate the gelatin and extract the water, then the methanol can absorb the water, leaving the IPA free to dehydrate more gelatin.

I couldn't think of any other water miscible solvents though. If gelatin is willing to take up some other solvent more readily, it might be possible to simply displace the water in the gelatin without necessarily absorbing it into the solvent.

Since the basic idea is just to dehydrate the gelatin, I wonder if there are any solventless approaches... vacuum chamber? oven drying? Not sure how friendly these would be to the fringe patterns.

jeff-blyth
Posts: 20
Joined: Sat Feb 18, 2017 9:41 am

Re: Dehydrating with methanol instead of IPA?

Post by jeff-blyth » Wed Jan 03, 2018 4:30 pm

[quote][/quote]

I think you are working with a paradigm which is quite faulty there. The ipa only penetrates where there is water and not where there is gelatin. Gelatin and ipa (and acetone) are not compatible but gelatin and methanol are very slightly compatible. It is not the desiccation that is the key issue but the formation of voids in the dark fringes that were swollen by water much more than the light-struck hardened fringes which were relatively unswollen. A vacuum chamber would just collapse the potential voids in the wet state, and so would an oven or hot hairdrier. [However I have had examples where a "dried" standard processed DCG hologram put in a vac chamber for ~10 minutes has lasted for years without any protection because the last traces of moisture were sucked out. So it is a good idea to put a good standard DCG holo under a vacuum for a while].
But what is wrong with my earlier suggestion of using 2(or more) methanol baths and a 100% ipa for your final bath? Alternatively dry acetone is not such a risk in Canada at this time of the year, if used sensibly. I think that the problem that caused the fire was due to it being heated in the final bath. A quite warm final ipa bath I think is usually used in commercial operations because it gives just that bit more brightness. But I would'nt risk it if you are just having a go as an amateur.

Din
Posts: 226
Joined: Thu Mar 12, 2015 4:47 pm

Re: Dehydrating with methanol instead of IPA?

Post by Din » Wed Jan 03, 2018 6:48 pm

jeff-blyth wrote:[However I have had examples where a "dried" standard processed DCG hologram put in a vac chamber for ~10 minutes has lasted for years without any protection because the last traces of moisture were sucked out.
Here in San Diego, where the humidity averages about 30%, and gets as low 10% sometimes, we too have had unprotected holograms last for years. The lower humidity "draws out" the water in the emulsion.
jeff-blyth wrote:A quite warm final ipa bath I think is usually used in commercial operations because it gives just that bit more brightness.
True. I keep my final alcohol temperature at about 70 C. But, as you mention, it takes a certain amount of care; the flashpoint of IPA, where the IPA spontaneously combusts, is about 80 C, so you need to keep a careful watch on the final IPA bath temperature. Don was always nervous about heating the IPA, so he blasted the plate from the last bath with an industrial heater instead!

pluto
Posts: 95
Joined: Fri Feb 05, 2016 2:06 am

Re: Dehydrating with methanol instead of IPA?

Post by pluto » Sat Jan 06, 2018 11:13 pm

Din, I think you might be mistaken on that last point. IPA spontaneously combusts at 400c and the flashpoint (lowest temperature that it will ignite at) is 12c.

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