[alt-photo] Re: Your Approach to Making Negs for Platinum Printing? Ideal Negative Contrast and Dmax?

[etienne garbaux]

Francesco wrote:

>Now that I'm
>venturing fairly aggressively into platinum, I'm very interested in hearing
>how you all approach making your negatives for platinum. I'm speaking
>specifically about in-camera negatives (no digital negs or other processes
>here). Achieving the ideal contrast for platinum is what I'm interested in.
>For silver, a negative with a contrast range of around 3.5 stops will print
>well on a grade 2 filter or paper. There is also a ideal negative dmax that
>some people use as a standard to shoot for but I'm not sure what that number
>is. As I understand it, platinum calls for greater contrast to take
>advantage of the longer tonal range of the platinum process.

Below are some observations I have made in the past (you will find 
others in the list archives, from me and others).  For the 
traditional Pt process, you want a negative with a density range 
("DR") of 2.0 or higher (I generally aim for 2.4) to get both Dmin 
and Dmax in the print.  Note that not all films available today will 
produce such a DR, no matter how you expose and develop them.

BTW, I encourage everyone to stop speaking of "stops" and "contrast 
range" -- much better to identify clearly what you mean and speak of 
"exposure scale" ("ES") and "density range" ("DR"), to make sure we 
are always keeping the distinction in mind.  On this, see my message 
of 11 Oct 2009, in the archive.  For example, while the ES of 
traditional Pt is around 2.1 to 2.4 (and, therefore, a negative that 
produces a full-scale Pt print will have a DR of 2.1 to 2.4), the 
full-scale DR of the Pt print itself is much lower -- only 1.4 to 1.7 
(the latter only with heroic efforts).

==========

>There are two things at work here: (i) matching the negative density 
>range ("DR") to the printing exposure scale ("ES"); and (ii) the 
>character of the exposure scale, however long or short it is.  If 
>the DR of your negs is too short to match the printing ES, you'll 
>get low-contrast prints with murky (but not very deep) shadows 
>and/or fogged-looking highlights.  But even if the negs have the 
>right DR for the process, the characteristic curve of the printing 
>process may be ugly.
>
>The standard long-scale Pt process has a very, very long linear 
>scale with symmetrical, gently rounded toe and shoulder, typically 
>printing the whole step wedge with some scale left over.  Therefore, 
>you need to use negatives with a very high DR to obtain all of the 
>available print zones with this process.  Photographers have not 
>typically made negatives this "bulletproof" since the late 19th 
>Century, so folks have tried a number of different methods to 
>shorten the Pt exposure scale (adding dichromates, hydrogen 
>peroxide, etc., etc.).  These tricks shorten the exposure scale by 
>raising the threshold exposure -- not really a very promising way to 
>go about it.  Anybody who has done serious sensitometry with the 
>process has seen the ugly characteristic curves the short-scale 
>versions of the Pt process produce.  I have yet to see prints made 
>using any short-scale Pt process that came close to the look of 
>"real" (long-scale) Pt prints.  Unfortunately, so many workers are 
>using the short-scale processes now that many people don't even know 
>what a good Pt print is supposed to look like.
>
>I commend to you an experiment:  Make some in-camera negatives with 
>a DR above 2.1 (try to hit 2.4 for starters), and print them using 
>the standard full-scale Pt process.  I bet you never go back to 
>digi-neg Pt printing again, and depending on how big you think 
>prints need to be, that you acquire one or more LARGE format cameras 
>or learn to make good enlarged negatives in the darkroom (not so 
>easy now that slow, blue-sensitive copy films are long gone).  If 
>you have no option besides digital, have a service bureau make some 
>2.4 DR negatives with an imagesetter using your files.

==========

>Think of it as mapping.  The scene you photograph has a certain 
>range of luminance values.  You want to translate, or "map," these 
>luminance values to useful negative densities, which can in turn be 
>mapped to the available reflection densities of your chosen printing medium.
>
>To do this, we start with the exposure scale ("ES") of the printing 
>medium.  Using calibrated step wedges, we see what range of 
>exposures gives the full range of printed tones the medium is 
>capable of producing -- any more exposure is indistinguishable from 
>the blackest tone, and any less exposure is indistinguishable from 
>the lightest tone (paper white, or close to it).  Now, if we want 
>the full range of tones the process is capable of producing to be 
>represented in our print [which may not always be the case], we know 
>that our negative must have a density range ("DR") equal to the 
>printing medium's ES.  So, we arrange to translate the luminance 
>values in the scene to the particular negative densities that will 
>produce the print tones we want to represent each scene luminance value.
>
>Not so long ago, we did this by adjusting our exposure and film 
>development, and then perhaps reducing or intensifying the negative 
>or masking it for printing, and finally by dodging and burning as we 
>printed.  It sometimes took all that, because we have to condense or 
>compress the 1,000,000:1 luminance range of the scene we 
>photographed (this is about normal for a sunlit scene) down to the 
>100:1 (or less) density range that a print can reproduce.
>
>These days, people who print digitally can use Photoshop to adjust 
>the mapping from the as-captured (or as-scanned) image file to the 
>negative that will be used to make the print.  This is much easier, 
>and also much more flexible, than doing it chemically or with 
>masks.  However, the goal is the same -- to translate or map certain 
>luminance values in the scene to the desired print density values, 
>using the negative as an intermediary.  Applying curves is how we do 
>this.  It's fundamentally the same as using the Photoshop tonal 
>controls (levels, brightness/contrast, whatever) to adjust a digital 
>capture for the desired print values (i.e., if you are just printing 
>digital images on paper), with two added wrinkles: (i) you have to 
>understand how the characteristic curve of the printing process 
>responds to the negative values, and (ii) you have to be able to 
>imagine how to "do it in reverse" since you are working on a 
>negative -- if you want the shadows to have more contrast in the 
>print, you have to increase the contrast in the lightest parts of the negative.
>
>In theory, you can map any scene luminance value (or digital 
>representation of a scene luminance value) to any available print 
>tone (with the caveat that the curve should be monotonic -- never 
>reversing slope -- unless you are after special effects reminiscent 
>of the Sabattier effect).  In my view, there is no substitute for 
>learning enough sensitometry/densitometry to really understand how 
>the mapping works, and then to test your processes to see how they 
>distort the mapping so you can correct for it.  It's not very 
>difficult, and once it is mastered you will truly have the chops to 
>get what you want out of your photographs.
>
>So, all that said, back to curves destroying negative 
>content.  Mapping is mapping -- the person who wants to represent 
>the surface of the earth on a flat surface has choices to make, 
>because there is no way to linearly reproduce the surface of a 
>sphere on a flat surface.  And as we learned in grade school, 
>cartographers have come up with hundreds of different ways to do it, 
>each one good for some particular task.  If you want to be able to 
>visualize comparative land areas, you use a different projection 
>than if you want to determine bearings from one place to 
>another.  The same is true for mapping tonal values in 
>photography.  So, the "right" curve is the one that produces the 
>results you want -- i.e., the one that maps the scene luminance 
>values to the print densities you want.  In general, one way I'd 
>advise folks NOT to do this is to copy someone else's curve "because 
>you're using the same process."  No two people ever use the "same" 
>alt process, because there are way too many variables to 
>control.  And no two monitors are the same, or scanners, or 
>printers, or Pt "emulsions," or coating techniques, or anything else 
>you use to make prints.  So, the only way to end up with a useful 
>curve for your process flow is to test and figure it out for yourself.
>
>Generally, one would like to calibrate one's monitor, then build a 
>curve for each printing process one uses so one can just adjust the 
>image on the monitor (as a positive), then let the computer figure 
>out what negative densities are required to map the monitor view to 
>the final print (though once again, the monitor has a considerably 
>greater luminance range than a print has density range, so it will 
>be a "rendition" of the monitor image, not a literal copy).  Only 
>you can build such a curve, after doing the 
>sensitometry/densitometry on your equipment and printing 
>processes.  There are aids available, but IMO one is much better off 
>gaining an understanding of the fundamentals and just doing it -- 
>just as people who really understood what they were doing always got 
>better results than people who "learned" the "zone" system by rote.
>
>So, if you have a curve that really does translate (transliterate 
>??) from your monitor to your prints, great -- it is not destroying 
>anything, but rather helping you to map values from your digital 
>image file to the final print, thereby allowing you to do your image 
>adjustment by eye rather than by figuring.  But if your curve 
>doesn't produce prints that are pleasingly rendered based on the 
>screen image, you need to change something.  You can futz around 
>with the process to try to match it to the curve you have, but 
>that's the hard way (and you may well not ever find a variation that 
>works as you'd like).  Better to adjust your printing process until 
>you get the most linear scale you can (for reasons I won't go into 
>here, having to do with producing the smoothest tonal range), then 
>developing a curve that translates from your monitor to your prints.
>
>The problem with the "short-scale" versions of Pt is that they have 
>much less linear tonal ranges than long-scale Pt.  You can 
>successfully map this, if you work at it, and thereby get correct 
>overall tonal rendering by using a curve that compensates for the 
>nonlinearity.  However, you still won't get the smooth transitions 
>that long-scale Pt can produce.  And since the gorgeous tonal 
>rendering is the real draw of Pt in the first place, why settle for 
>something less just because one would prefer to avoid dealing with 
>how to make digital negatives of sufficient DR?  Particularly given 
>the cost of the Pt process, I just can't see why one wouldn't use it 
>to its full advantage -- which IMO requires using the long-scale process.


Best regards,

etienne