Author: Paolo Saccheri

What printer settings should be used for creating digital negatives?

Many print makers ask what are the correct printer settings to use to print their digital negative. The real answer is that there is no fixed true answer. It all depends on your process, i.e. the sum of all the variables you have when printing. 

Each printer – which is a variable of the process – has a set of inks and a printer driver that will give you a different print from another printer, and so a different UV filtering ability. We may certainly say that each printer combined with the printer settings and the software you use to print, plots a different UV filtering curve which means your result will be different if you change something.

In a specific printer driver you can choose from many different settings like: the color space, the paper type, how it manages colors, etc. and each setting changes the rendition of colors in the print and so the UV filtering curve (more on that later on).

In my tests with my printer Epson P600 I used different settings in the printer driver and also used different softwares to print from (Photoshop, GIMP, Adobe Color Printer Utility) to see the differences in the final print.  Each test gave me a different result.

Inside Photoshop I have printed 7 strips of a 21 grey step tablet on a transparency film, changing paper type and color management settings in the printer driver for each print, in order to see what differences in density (UV filtering) those two settings can give.

I tested different paper type setting while printing on my transparency film:

• Premium Luster
• Premium Semigloss
• Paper Glossy
• Premium Glossy

And different color management:

• Photoshop manages color
• Printer manages colors

In my test, for my process, i.e. the sum of all the variables I have, including the printer, Printer manages color wins for now together with Premium Glossy paper. My decision was taken upon several considerations including the exposure scale I wanted to get, which is related to paper white point (more on that later on).

It is a test you may need to make if you don’t have paper white in your print, or if the correction curve you get out of your test print is too strong/rough. You may be able to find out, during the calibration of your digital negative, if one or more printer settings combined make the print of your negative denser than another or the correction curve smoother, which is better. I also tested other settings inside Photoshop, like the Color Mode “Adobe RGB” or “NO color management“. Some prefer using NO color management, but for my process it is not a good choice.

The actual version of GIMP (at the moment of this writing) doesn’t allow you to choose whether “GIMP manages colors” or “Printer manages colors”, the way you can choose inside Photoshop.

Adobe Color Printer Utility (also known as ACPU) is a system used to print with NO color management. The problem I had (inside Windows operating system) is that the print was done at the upper and leftmost point of the film and I couldn’t find the way to print it more centered, nor in 1:1 scale. So, not good for me.

How to test and select the best printer settings

To find your best printer settings you need to reach the point in the calibration process where you test print the step tablet to generate the correction curve.

Before that, following what I teach in my video course Digital Negative for Alternative Photography, you need to have done the following steps in the calibration process:

• Found your Standard Exposure Time
• Found your Optimal Color Blocker
• Found paper white at the right point
• Printed the negative of a plain 256 step tablet file with your optimal color blocker on top

The best settings are the ones that give you the smoothest correction curve, given you have paper white.

As you will be able to find through experimentation, if you use EDN calibration system, is that the EDN Optimal Color Blocker helps to have a smoother correction curve because of how it is engineered.

In my case the best negatives are the last two (highlighted in yellow), printed with GIMP and with Photoshop. You can notice that the correction curves are in some parts already almost linear (adjacent to the diagonal line, which is where the correction curve will have to go after the linearization). 

It is not important for you to copy my settings because as I said they are right for my process (which is the sum of all my darkroom variables, not only the emulsion type I use) and so it might be better for you to do your printing tests if you want to get the best out of your calibration process.

I printed the same file using different software. It is a plain 256 step tablet with the same Optimal Color Blocker LUT on top. As you can see, the colour reproduction on the transparency film is very different, as well as the correction curve coming out from a test print made in cyanotype using those negatives.

So, if you want to go into such detail, try to have fun in these tedious tests! 

Remember that it can be frustrating at the beginning but very rewarding at the end.

Always remember that the calibration process for your digital negatives needs to be performed keeping firm all your darkroom and printing variables (including the Relative Humidity, paper humidity) you have while performing your tests.

This is an external resource of the video course Digital Negative for Alternative Photography. You can read more about it in this website clicking HERE.

Why do we colorize digital negatives?

At the beginning of the digital negative era, around the early and mid ‘90s, the inks of the digital printers had poor UV filtering ability compared to what you find today.

For printing in some Alternative Photographic processes that have an extended exposure scale like platinum palladium you need a very dense negative to block UV light so to have paper white in their very long exposures.

Dan Burkholder introduced the use of a colored negative in those years, because color inks had more UV filtering ability than the black ink at that time. He introduced a simple way to do it, but since then a lot has changed although it is still a valuable concept today.

An evolution in colorizing digital negatives.

The first technique to colorize a negative was by adding over the digital negative image, a new layer filled with a specific color, normally greenish or reddish chosen by experience.

An evolution happened to find a more precise color. With that you could find the best color matching your own printing process which is the sum of all your darkroom variables, not only the emulsion type you use, and give you a better result.

Mark Nelson created a calibration system called Precision Digital Negatives (PDN) where you can test what color you have to use with your process for best UV filtering property. His patented Color Palette only uses primary R, G, B colors, pure or mixed together, and no black. To make this system work, he tells you to use the printer setting NO color management so the printer uses the R, G, B inks only and NO black ink. His system is very well known and appreciated for the precision of its results.

I tried it with classic cyanotype and printed the Color Palette using my Epson P600. I could not reach paper white in my test print using the standard (zero) ink level (quantity) while printing the Color Palette on the transparency film, so I had to raise my ink level through the printer driver (not all the printers allow you to do that) and finally had paper white.

Nowadays the inks of the best inkjet photographic printers are of a very high quality and have a very high UV filtering ability, specifically when they are pigment based inks.
The printer drivers use modern technology and science to define how to mix all the inks to smoothly produce the tone you want, and the black inks give very high densities, enough to print a digital negative for classic cyanotype without having to raise the ink density level; on the contrary, you may find yourself lowering it a bit, depending what printer you use.

Peter Mrhar created a calibration system that I also use, called Easy Digital Negatives (EDN). The EDN Color Blocker free tool makes you use an HSB color image to define, with precision through a test print, the Optimal Color Blocker correct for your process.

There are many print makers using EDN that are not clear how the Color Blocker tool works, so I will give a short explanation.

The tool reads your HSB test print, like mine in classic cyanotype, and goes through the following important automatic checks:

1. what colors give you “inversion of tone” (a) in the print and exclude them (e.g. color columns from 0 to 130 in the image above).
2. what specific color, among those remaining available, gives you the most extended range of tones (b) to help the calibration (column 350 in the above image).

a) Being clear that the dark tones in a negative produce light tones on a print and lighter tones in a negative produce darker tones on a print, you have an “inversion of tone” in your print (someone calls it “solarization”) when a dark tone in your negative blocked less light than a lighter tone. This prevents your photo from having smooth gradients and faithful reproduction of tones.

b) When the EDN Color Blocker system chooses the color with the most extended range of tones means that you have more color difference/tonalities to reproduce the tonalities of your photo. Consider it as if you want to make a b/w pastel painting having 3 pastels only (black, medium grey, white) or if you have 6 different pastels in tones of grey instead. Of course having an extended range of pastels will give you better smoothness and transitions in the shades of your painting.

Without those two checks, a dense enough but wrong color may give you bad prints without you knowing it or understanding how to solve the problem.

This colorizing system gave me more than sufficient density to print my classic cyanotype with the standard (zero) ink density level of my printer Epson P600, since it uses all the inks including the black ink cartridge which in my case is a pigment based ink.

I could actually use a negative value of ink density in the printer driver (maybe -5, or -10) saving ink and faithfully print my cyanotypes.

As a matter of fact, having a digital negative that was a bit denser than needed created an area of paper white wider than desired (Image 4), so I decided to extend the tones of my print using some citric acid in my development stage (Image 5). This worked well with cyanotype, for other processes you might have other ways to control the general contrast, or you may choose to reduce your ink density if your printer allows that.

I find another very important advantage in the EDN Color Blocker tool. It lets you download your colorizing layer not only as a Gradient Map but also as a LUT file, and inside the LUT file the color hue chosen as your Optimal Color Blocker changes to adapt to the different areas of your photo (dark areas, midtones, highlights) and doing so you have the best color choice possible, creating the premise for a milder correction curve when calibrating your digital negative, and a mild correction curve means less artifacts and best precision in tone reproduction.

Generally speaking, the LUT file of the Optimal Color Blocker performs as a former correction of your negative, so that you’ll need a very light calibration curve. That curve depends also on the printer settings of your choice while printing your digital negative, that will be the subject for another article.

This is an external resource of the video course Digital Negative for Alternative Photography. You can read more about it in this website clicking HERE.

• I coated a sheet of paper using a rod and very little emulsion (0,0025 ml/cm2) down to where I drew the pencil lines. I cut the sheet in four strips when dry. 
• Room temperature was 22 deg C and Relative Humidity 74%. 
• I waited 20 minutes from coating and printed the first quarter of the coated sheet (Test strip 415c) for 1 minute (a shorter exposure time than my standard so to better see any color variation when comparing it with the other prints). 
• I covered a part of the coating with an opaque material to have a non exposed area where to check fogging.
• I waited 40 minutes from coating before printing the second quarter of the sheet as above (Test strip 416c).
• I waited 60 minutes from coating for the third quarter as above (Test strip 418c).
• I waited 80 minutes from coating for the fourth quarter as above (Test strip 417c).

P.S. yes I mismatched the strips already numbered when printing so they are not in sequence, but correct.

At the end of the test I could see there was no difference in dMax (color density) in the four prints and the fog under the covered part was pretty similar and almost absent.

In my conclusions there is not much difference if you wait for 20 or 80 minutes to print after coating. 

P.P.S.  I always suggest not to wait too long from coating to printing otherwise fogging may become evident in some circumstances (depending on quantity of emulsion used and R.H. of your place) and your paper white may be less white, or gone. 

I tend to always wait from 45 to 60 min for consistency in my darkroom variables, the base for a perfect digital negative.

This is an external resource for cyanotype printing of the Digital Negative video course. You can read more about it clicking HERE.

I used only acid free papers for quite a long time, before I started buying Arches Platine, a pure cotton rag with no alkaline reserve that gives me wonderful results with blue and turquoise shades.

Acid free papers such as watercolor papers often give very dark blues, even darker than Arches Platine and they are much cheaper, but they tend to bleach out when printing in cyanotype unless you adopt some countermeasures.

You have two ways to do so:

• pre acidify your sheets of paper before using them for printing
• compensate for the alkaline buffer when developing and washing your print.

I never pre acidify my paper because I don’t want to spend time working twice on a sheet of paper, but it might be the best practice, in fact if you pre acidify you end up printing with a neutral paper and this makes things good and easy.

If you coat your buffered paper the way it comes and print on it when the emulsion has dried, let’s say after one hour or so, you can perfectly compensate for the alkaline buffer when you develop and wash your paper immediately after printing.

In my tests I found that the alkaline buffer of Canson XL Aquarelle (or Watercolor, name depends on what market it is sold) can be perfectly compensated using 0,3 g/l of sulfamic acid put in all the dev. and washing baths, for at least 15 minutes, but 20 minutes are better for a complete wash.

Before Canson, I also used other buffered papers such as Fabriano Accademia and Caballo 109, and I always compensated for their alkaline buffer during wash.

Sulfamic acid has good properties when used with paper because it doesn’t interact badly with the paper itself and has no smelling fumes (unlike chloridric acid that I used when I began printing). But sulfamic acid is not super soluble so you need to warm up some water, up to 60-70 degrees Celsius (140-160 F), and then pour it on your acid crystals inside a capable container, then stir for a few minutes until complete dissolution.

I make a rough 10% solution (not exact in chemical practice) using 90 g of sulfamic acid crystals and 900 ml of water (0,9 liter).

When developing and washing the print that you have made on Canson XL Aquarelle (Watercolor) you need to put 3 ml of the sulfamic acid solution you have previously prepared per each liter of water you put in your trays.

For 20×30 cm (8×12 inches ca.) prints on Canson and classic cyanotype my 3 small trays are configured this way:

1. 2 liters of water with 3 ml/l (in 10% solution) sulfamic acid, constantly rocking by hand for 1 minute (there is a lot of wash off).
2. 2 liters of water with 3 ml/l (in 10% solution) sulfamic acid, rocking by hand for 4 minutes.
3. 2 liters of water with 3 ml/l (in 10% solution) sulfamic acid, rocking (but less) by hand for 15 minutes.

You need to change the water in the first tray for each print (it gets very dirty) and you can use the water inside the second and third tray (with two liters of washing water each) for a maximum of three prints, this is because during washing the acid is slowly neutralized while compensating the alkaline buffer of the paper, so you need to have fresh water and acid to be always effective in washing the print and getting rid of the alkaline buffer.

If you want to use another type of acid, like citric acid (the worst option is chloridric acid), you’ll need to experiment with the quantities I suggested, since each acid has a different pH when diluted in water and so a different compensating ability.

If you want to use white vinegar you need to experiment too, you’ll need way more quantity.

Everything must be tested, defined and then kept consistent in your printing process, that is the base for a perfect digital negative.

This is an external resource for cyanotype printing of the Digital Negative video course. You can read more about it clicking HERE.

Washing your cyanotype in the best way is very important in order to have a print that will last beautifully.

If you don’t wash enough, some emulsion will remain inside the paper and it will show up in time as a yellow cast in the highlights. 

If you wash too much, you risk to wash off a bit of the darker areas of your print and so to reduce its overall contrast.

Water temperature, water pH, washing time, speed of agitation (rocking) are all factors that may give you a difference. You want to find your own way to develop and wash and keep it consistent, from the first test prints during the digital negative calibration to your real photo prints, because also from that depends the reliability of your digital negative calibration, and at the end the quality of your print.

I found that for my process with Arches Platine (a process consists of the sum of all the darkroom and printing variables including emulsion type, paper type, relative humidity, type of coating, etc) the best washing time was 20 minutes in total. 

My tap water is alkaline and to compensate it I need to use a little citric acid as follows. This is valid only for me, you need to check the pH of your tap water, for that I suggest you to use the liquid tests for aquariums which are more reliable than the paper strips. Also, I use a certain quantity of citric acid in the first development tray to widen the exposure scale in my prints but I’ll write more on that in a specific post.

For a 30×40 cm (12×16 inches ca.) print on Arches Platine and classic cyanotype my 3 trays are configured this way:

• first tray: 2 liters of water with 5 ml/l (in 10% solution) citric acid, constantly rocking by hand for 3 minutes, print face up to avoid air bubble formations, with a continuous and rather quick (but not too much) rocking at least in the first minute when developing occurs to prevent staining from bleeding.
• second tray: 10 liters of water with 0,3 ml/l (in 10% solution) citric acid, I use a small submerged aquarium pump because I get bored, (hence the 10 liters, otherwise 5 liters are enough if my pump can stay beside the print inside my tray) for moving water for 3 minutes, print face down, to clear most of the emulsion.
• third tray: 5 liters of water with 0,3 ml/l (in 10% solution) citric acid, gently rocking by hand from time to time for the last 14 minutes, print face down.

For smaller prints like 25×25 cm (10×10 inches) I use 2 liters, 5 liters and 5 liters respectively in my 3 trays and if the prints are smaller I reuse the water of the second and third tray for washing more prints. I always change the water in the first tray for each print.

Washing for a total of 15 minutes was also good but the paper white was best at 20 mins, so that’s my washing variable defined for a perfect digital negative.

This is an external resource for cyanotype printing of the Digital Negative video course. You can read more about it clicking HERE.