Perceptual (visual) adjustment of curves? Guidelines?

[Daniel Balfour]

I bought Reeder & Hinkel's book - Digital Negatives. The process they describe for making corrective curves involves first printing a step-tablet with a "starting curve", then contact printing that tablet onto photo paper, scanning it back into Photoshop, and measuring/correcting the differences in another "adjustment curve". In theory, this sure sounds interesting. I'll be trying it in the next few days. However a question comes to mind:

What if you cannot scan your "print" back into photoshop, such as in the case of Ambrotyping or tintypes?

What then?

Is there a way to visually adjust the curve simply by "looking" at the glass positive?

Would it make sense to take a digital photograph (in some controlled environment) of the finished "print" and then try to map those values to the initial printed inkjet tablet?

Would love to hear some theories.

Daniel

 

[mkochsch]

I'd be really interested to see if a digital negative could do an ambrotype justice. But, that aside, maybe you need to be using your scanner in transmissive mode and not reflective. Then again ambrotypes are usually viewed on a black background (reflective) aren't they...can you photograph the tablet with with a digital camera? That should show the "relative" differences between steps and give you a rough idea of where you need to curve.

 

[Ron-san]

I bought Reeder & Hinkel's book - Digital Negatives. The process they describe for making corrective curves involves first printing a step-tablet with a "starting curve", then contact printing that tablet onto photo paper, scanning it back into Photoshop, and measuring/correcting the differences in another "adjustment curve". In theory, this sure sounds interesting. I'll be trying it in the next few days. However a question comes to mind:

What if you cannot scan your "print" back into photoshop, such as in the case of Ambrotyping or tintypes?

What then?

Is there a way to visually adjust the curve simply by "looking" at the glass positive?

Would it make sense to take a digital photograph (in some controlled environment) of the finished "print" and then try to map those values to the initial printed inkjet tablet?

Would love to hear some theories.

Daniel

Daniel-
You should be able to read the tonal values from an Ambrotype (or alumitype, or tintype) just like you would do for any platinum or palladium print. Put the Ambrotype on a flatbed scanner, scan it, adjust the black and white endpoints, and use the Photoshop eyedropper to read the K (%gray) values. Just as described in the book.

However, there is not much point in trying to make an Ambrotype from a digital negative. The wet plate process is WET. You cannot place a negative (or positive) on a wet plate and make a contact exposure. (at least I don't see how it can be done).

What I have done, instead, is to print out a digital POSITIVE (on the usual Pictorico transparency material), backlight the positive, and photograph that onto an alumitype. It works very well and you are then free to make a wetplate positive of essentially any image in your image library.

The only trick, I find, is that the wet plate process is very contrasty. So I had to make a flat, low contrast digital positive. To lower the contrast I opened the Curves dialog box, grabbed the black end of the curve, and dragged it in a direction that caused 100% black to become a darkish gray. At the same time I grabbed the middle of the curve, lightened the shadows and darkened the highlights, to make the midtones flatter.

By empirically making a few positive transparencies, each a bit more low contrast that the last, and making an alumitype from each, I was able in an afternoon to come up with a flattening protocol that resulted in good alumitypes. I never got around to actually photoing and scanning a step tablet or other more scientific approach.

Try it. I bet you will have fun. It means you can make alumitypes (ambros, whatever) any time of the day or night and of any subject.

Cheers, Ron-san

 

[Daniel Balfour]

However, there is not much point in trying to make an Ambrotype from a digital negative. The wet plate process is WET. You cannot place a negative (or positive) on a wet plate and make a contact exposure. (at least I don't see how it can be done).

Ron,

Actually I'm talking about using Liquid-Light (or more accurately Ag-Emulsion) which is designed specifically for this purpose (hence "Ambrotypes/Tintypes" and not "wet-plate"). I've yet to try it, but a recent phone call to Rockland Colloid left me very optimistic.

At this point I'm still working with silver-gelatin as I haven't yet completed the process start-to-finish. Once I get it, I will definitely be making the leap to Ambros.

I look forward to scanning/uploading my results!

Thanks for the tip!

Daniel

 

[Kerik]

Just to clarify, the terms ambrotype and tintype were coined in the mid-1800's with the wet plate collodion process, so Ron is correct. They have no inherent link to liquid light and its cousins. Those modren processes have borrowed the terms for their use.

Also, although I've not used it myself, I've talked to several people who have tried the Rockaloid stuff and have been very frustrated with the results.

 

[Daniel Balfour]

Just to clarify, the terms ambrotype and tintype were coined in the mid-1800's with the wet plate collodion process, so Ron is correct. They have no inherent link to liquid light and its cousins. Those modren processes have borrowed the terms for their use.

Kerik,

My bad then - I didn't realize that. I was under the impression that collodion was merely a process, not relating to a particular result (ambro/tins, etc).