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JOSarff
02-27-2011, 05:51 PM
My memory has failed me. Which is the correct vehicle for thymol? Ethanol, 2-propanol (pure), 2-propanol (70%) or water?

Joe

Hexavalent
02-27-2011, 06:03 PM
Isopropyl works just fine. I prefer to use 100% (or electronics grade 99.953). Thymol is insoluble in water.

JOSarff
02-27-2011, 06:08 PM
Thanks Ian

Photo Engineer
02-27-2011, 06:16 PM
As long as the alcohol is not denatured, either can be used.

PE

dwross
02-28-2011, 09:02 AM
A tangential note: Thymol should be considered an unnecessary ingredient for almost all emulsions we're likely to make and use. It's a preservative, and basically a carry-over from the days before reliable refrigeration and when gelatin was more likely to be contaminated with odd bacteria. If you make small, frequent batches of emulsion and use them within a week or two, you won't need a preservative. I strongly recommend this for two reasons.

1) Making good emulsions is all about practice, practice, practice. If you make up big batches, infrequently, you'll likely never learn the 'tricks', which are nothing more than the application of experienced observation.

2) The characteristic curve of an emulsion gradually changes during long storage, preserved or not. Any attempts at standardizing to a contrast grade will be made much harder unless you also standardize to a pre-coating storage time range.

d

Photo Engineer
02-28-2011, 10:49 AM
There are several factors to consider here:

1. I make up gelatin at 20% and 10% in advance for storage to reduce darkroom prep time. The preservative is useful here. I can keep preserved gelatin for 6 months or so and hope to increase this to a year or so soon with a wider range of preservatives.

2. Anyone who knows biology, knows that gelatin is a good growth medium for all sorts of micro-organisms. We are warned not to work with our emulsions and gelatin solutions if we have a cough or strep or any form of illness like that. This can "turn" an emulsion or gelatin just about overnight.

3. The experiments that I showed at several of my workshops were from emulsions up to 6 months old and the coatings were over 1 year old. Curve shape looked pretty good to me. I could not have kept the emulsions for 6 months or more without thymol.

4. I make my standard emulsions in 120 - 500 gram batches and often mix them, they are so much alike. I keep a 1 L can of the blends for my common coating checks to refer back to when I make experiments. If I don't know where I have been, I don't know where I am going! :)

5. Finally, use of Thymol or any preservative is useful, as you then have a coating formula which includes this chemical and therefore does not need a big change when you change workflow to included older emulsions and gelatin solutions.

This all summarizes why I teach the use of preservatives in my workshops!

PE

Hexavalent
02-28-2011, 11:00 AM
I would tend to think that preservative not only serves a purpose in 'wet' emulsion, but also adds a measure of protection to the finished, dried product. Better safe than sorry AFAIC. Besides, that certain Thymol aroma is one of the darkroom fragrances that tells me I'm doing something :)

Photo Engineer
02-28-2011, 11:36 AM
Well, the Thymol eventually evaporates out of the finished, dry coating, but it can help. It is present in packaged sheets and the preservative is certainly present in commercial products. If you open a package of Ilford paper, you can smell the phenol which is what is used as a preservative in their B&W papers. That is so strong and toxic when used in the home darkroom that I don't suggest it, but it is used by Ilford and Schoeller as well in large scale operations. Kodak does not use either Thymol or Phenol. They used equally potent materials. I'll comment on them soon.

However, there is another important fact involved in this that I did not mention earlier.

All batches of fine photo grade gelatins are packed with an assay, just like fine chemicals. Only in this case, it is a bioassay that includes things such as tuberculin bacilli, staph, strep, E. Coli and etc per unit weight. This means that the dry gelatin contains a certain amount (printed on the assay), per specified unit of dry gelatin. Well, when you mix your gelatin in warm water those microorganisms begin to multiply unless you stop them. I don't know about you, but I don't like handling gelatin without some sort of preservative there to retard their possible growth!

PE

Hexavalent
02-28-2011, 11:41 AM
As far as microbes are concerned: "there's always room for Jello!":laugh:

Vaughn
02-28-2011, 12:02 PM
And us carbon printers toss in a bunch of sugar, too!

Does the alcohol itself help keep the beasties away (I use about 10ml of 100% isopropyl per 750 ml of glop)?

And does the exposure time under the UV lights (even tho it is not the deadlier UVC) help kill the beasties?

Hexavalent
02-28-2011, 12:21 PM
And us carbon printers toss in a bunch of sugar, too!

Does the alcohol itself help keep the beasties away (I use about 10ml of 100% isopropyl per 750 ml of glop)?

And does the exposure time under the UV lights (even tho it is not the deadlier UVC) help kill the beasties?

Rotten carbon glop is one evil smell! YUK! Had it happen once, and now everything gets a dash of thymol.

Isoprop is an effective bacteriocial only at higher concentrations (i.e. 70% used in prep-pads), so I doubt it does much for 'glop'. A thin layer of isop floated atop gelled glop does provide a barrier against critters - it can be poured off before use.

There are plenty of beasties that thrive in full sunlight, so I doubt a typical exposure is going to have a major disinfectant effect. Post-printing hardening with an aldehyde will sterilize a carbon print, it was a fairly common practice in the "old days"

Photo Engineer
02-28-2011, 01:12 PM
Vaughn, the alcohol at that level will be rather mild in effect against the beasties IMHO. The UV will not have much effect due to the black blocking power of the carbon (imagewise) but it will also have some effect.

Thymol, Phenol and Kathon are better, but Kathon comes with some metal preservatives and you just about need EPA approval to use it. You can burn yourself with Phenol, and its sale is restricted in many states. That is why I use Thymol and why I am working to find another preservative.

These comments about preservative action of IPA and UV are just guesses based on some limited experience.

PE

Vaughn
02-28-2011, 01:24 PM
Thanks -- I just won't count on IPA and the UV. Unless the IPA stands for India Pale Ale, which needs to be taken internally on a regular basis for its optimal effect.

JOSarff
02-28-2011, 04:44 PM
As long as the alcohol is not denatured, either can be used.

PE

Well, I made a batch of 10% thymol in 95% everclear (what I had) and put 1 drop per 20g of 10% gelatin at 60C and came up with a yellowish lump about th size of a large packing peanut smelling of thymol. It now hangs in my truck as a deodorizer.

Ummmm, what happened. Gelatin too hot?

Joe

Hexavalent
02-28-2011, 05:02 PM
Joe,

Did you add it drop by drop, or dump it in? If you dump cold alcohol into gelatin, it can coagulate, though FMO, it usually melts/clears within seconds. Was there hardener present? Did you arrange your darkroom into the ideal feng-shui configuration? :)

JOSarff
02-28-2011, 05:37 PM
Joe,

Did you add it drop by drop, or dump it in? If you dump cold alcohol into gelatin, it can coagulate, though FMO, it usually melts/clears within seconds. Was there hardener present? Did you arrange your darkroom into the ideal feng-shui configuration? :)

Drop by drop by drop and the finished gelatin was going into a former hot & sour soup container (washed first). When I saw the lump, I fished it out immediately, not giving it a chance to melt/clear.

I'm not sure about the feng-shui, is that like foo-young :munch:, but our orange tabby Ozzy did wander through and didn't react, so it did pass the CAT scan.:whistling:

Photo Engineer
02-28-2011, 06:17 PM
Joe;

We use Everclear for a lot of things in coating and making and therefore it should not be the source of the problem. Having denatured alcohols may cause this kind of thing depending on denaturant, and that is why I warned against them, but Everclear has been shown to be safe at rather high levels AAMOF. Did you try a PET scan? :D

Seriously, I have no idea. I have never had that problem, but I always add it right after making or preparing gelatin or Silver Halide, and I believe that I have always added it at 40 deg C.

PE

Vaughn
02-28-2011, 06:24 PM
The literature I have read recommends not getting the gelatin over 120f -- about 50C.

Photo Engineer
02-28-2011, 06:48 PM
Well, thinking about this for a bit, I realized that I use about 5 - 10 drops in 500 grams of 10% gelatin. So, this is way more than I usually use. Looking back at my notes, this is what I recommended.

PE

JOSarff
02-28-2011, 07:09 PM
Well, thinking about this for a bit, I realized that I use about 5 - 10 drops in 500 grams of 10% gelatin. So, this is way more than I usually use. Looking back at my notes, this is what I recommended.

PE

I pulled the figure from my notes, 6 drops per 120 g of emulsion/gelatin. since I was making plain gelatin to use as diluting gel after the mix, I was adding the preservative.