Could this be a real direct positive emulsion?

[psykodaddy]

Hey folks,

long time no see (and no light to my emulsions)

Yesterday I stumbled across a patent (attached)

I was wondering if that could be a working direct positive emulsion finally?

Any thoughts from theory, or better practice?

I miss three chemicals, so I can't test it right now...

On page 2 under "example" it reads:

 

[Donald Qualls]

Seems a little, um, annoying to make. Assuming that's saturated ammonium hydroxide (not the 3% we get in the cleaning aisle at the supermarket), you'd need to perform those steps involving it with positive pressure isolation suit. Even after diluting the NH3OH into the water, you'd have something like 15% strength, which is five times what will burn your sinuses.

There might be a good reason we don't see this every day (instead getting the chemically fogged to the turnover point self-reversing Harman Direct Positive, when available).

 

[Donald Qualls]

In fact, come to think of it, ammonia is a known foggant; this might be the underlying patent for papers like Harman Direct Positive. The ammonia can be handled in a factory setting.

 

[psykodaddy]

I have the usual 24.9% ammonia here. I'm not a real chemist, just fooling around with recipes since some years.

But I totally know that this try will involve my full mask plus vent

I guess/hope that this formula is calling for that concentrated ammonia.

I'm looking for a direct positive emulsion for my home lab so long! Reverse developing is such a pain and unconsistent. I just want my plates to be positive!

If you don't have any suggestions, I'll try this way in some days. Just waiting for the missing chemicals to arrive.

 

[psykodaddy]

Just thought about noodling and washing this emulsion? Usually I do that, but don't know if it's good here...

 

[Lachlan Young]

There might be a good reason we don't see this every day (instead getting the chemically fogged to the turnover point self-reversing Harman Direct Positive, when available).

Harman DPP uses a nucleating agent as far as I am aware - this patent seems to be suggesting incorporating a chemical fogging agent (thiourea) to do what would otherwise have been done on older emulsions using a fogging exposure. There is quite a bit on here from Ron Mowery that goes into detail on the practical mechanics of direct pos emulsions - suffice to say there are better/ more efficient ways, if you have organic synthesis capacity available.

 

[psykodaddy]

I saw some posts from Ron about that...but he was far beyond my skills. I don't even understand what he did without thinking about

The formula I found in this patent just looked to me like something I'd be able to reproduce in my home lab.

Ammonia and thiourea as a fogging agent sounds pretty simple to me. What about the hydrobromic acid?

 

[Lachlan Young]

I saw some posts from Ron about that...but he was far beyond my skills. I don't even understand what he did without thinking about

The formula I found in this patent just looked to me like something I'd be able to reproduce in my home lab.

Ammonia and thiourea as a fogging agent sounds pretty simple to me. What about the hydrobromic acid?

I think I can see what the formula is attempting to do - it looks awfully like an SRAD with some attempt at getting a sufficiently 'chaotic' crystal structure such that it has high internal sensitivity, thus under specific exposure and process conditions, it'll produce a direct pos image. Very primitive as far as DPPs go in other words - but all DPP emulsions are complicated and challenging creatures - and it seems that critical precipitation details have been omitted from that patent. Ron gave essentially an ELI5 level summary on direct pos (and noted that he hadn't worked directly with the emulsions), and if that was too complicated for you, then it might be not worth investigating further at this stage in your emulsion making. Reversal processing a normal neg-working emulsion is overall going to be less of a headache.

More to the point, do you understand the dangers posed by the HBr and do you have appropriate safe handling measures in place?

 

[Ivo Stunga]

I'm looking for a direct positive emulsion for my home lab so long! Reverse developing is such a pain and unconsistent. I just want my plates to be positive!

Why inconsistencies and what are they precisely?
When I reverse film the only inconsistency besides me is temperature (must be the same across all chems), time and agitation frequency. All easily controlled.

 

[psykodaddy]

Thanks for your thoughts on that, folks!

@Lachlan Young I'll work with full mask, appropriate gloves and ventilation. Hope that's enough

This will be my last try to get a direct pos emulsion...after that I'm going back to reversing

@Ivo Stunga I'm still not sure where my incosistencies came from. I've tried too many new things at once, I guess. Do you have a good way of reversing to share, maybe?

 

[psykodaddy]

BTW: @Lachlan Young seems like I'm blind...can't find that easy summary from Ron about direct positive

 

[Ivo Stunga]

Thanks for your thoughts on that, folks!

@Lachlan Young I'll work with full mask, appropriate gloves and ventilation. Hope that's enough

This will be my last try to get a direct pos emulsion...after that I'm going back to reversing

@Ivo Stunga I'm still not sure where my incosistencies came from. I've tried too many new things at once, I guess. Do you have a good way of reversing to share, maybe?

If interested in my film reversal workflow, I could and have shared here and there. But not in an separate topic.

 

[koraks]

Why inconsistencies and what are they precisely?

Going out on a limb, the base material when working with self-made plates is just not as consistent as the film you're used to working with. Add to this the idiosyncracies of real-world exposures combined with the probable limited spectral sensitivity of OP's self-made plates, makes it really, really hard to tell how a particular image will come out. Trying to somehow calibrate this process to consistently yield plates of the desired contrast given a variety of scene brightness ranges, spectral distribution of light etc. will be challenging to the point of being impossible. Keep in mind also that when shooting plates you're shooting one image at a time and the investment in each image far exceeds what you invest in a typical frame on a roll of film. Which means that if you walk away with a couple of nice shots on a roll, but also a few that just came out overall too dark or with blown highlights, you'd still likely consider it a success. Whereas if you shoot 6 plates on a day and 4 end up being total failures, it's an investment of hours of work down the drain.

I think these realities should be kept in mind when interpreting OP's questions. Shooting plates, and in particular fairly rudimentary self-made ones, is really a very different ballgame than running a roll of factory-made film through a camera.

 

[Ivo Stunga]

Indeed and agreed - too many variables to account for with DIY plates, never thought of this.

 

[Lachlan Young]

full mask, appropriate gloves and ventilation

I still think you are underestimating how potentially dangerous it is. It is one of the strongest mineral acids and can do far more potential harm than something like HCL. A properly equipped lab with an appropriate fume hood would be the minimum, not a home experimental setup.

The difficulties (costs) of working safely with HBr probably played a role in the reformulation of HC-110 a few years ago. Like a lot of potentially dangerous reagents, risks from it can be mitigated if the scale of demand is sufficient to recoup the costs of handling it safely.

easy summary from Ron about direct positive

Here are three of them. The relevant patents that cover making suitable core-shell emulsions are readily found. Many of them would probably need quite a high level of process control at precipitation (ideally computerised).

particular fairly rudimentary self-made ones

Strong agreement here - unless they're coated with a sufficiently precise instrument (coating blade etc) and the uneven edges cut off and discarded, evenness of coating would be my first suspicion for many of the reversal defects - especially if they're pour-coated.

 

[psykodaddy]

My lab is pretty rudimentary compared to a "real lab", that's true.

I'm still in the beginning of plates, but have the minimums around.

I can control heat, stirring, coating, light, pump speed, ventilation.

Coating rods and a blade, syringe pump, magnetic stirrer with temp control, heating plates for coating, personal safety, digital scale, and more equipment.

You guys would wonder what else to find here

I was able to put together a nice home lab over the years.

I still miss practical experience and chemical knowledge for making good emulsions.

When I've cooked the soup from that patent, I'll share my wisdom

 

[psykodaddy]

Here are three of them

Thanks for these! Two were new to me and made me realize that I can't reproduce such emulsions in my little lab.

 

[Lachlan Young]

home lab

That's specifically what is concerning me about you working with the HBr.

 

[NedL]

That's specifically what is concerning me about you working with the HBr.

After reading about this, add yet another that I won't work with at home