Calibrating QTR curves for digital negatives

[dalton]

Hey there,

I'm wondering if anyone can help out with the problem I am having building my QTR curves. I am trying to create a curve for Pd using a Pictorico OHP negative. I have a bit of experience with QTR as a standard inkjet RIP, but this is the first time I am delving into the world of digital negatives.

I have been testing different curves for about two weeks now without much luck. I have all of the books (Reeder& Hinkel, Arentz, Burkholder) and I have read the recently published PDF from Ron Reeder's site as well as the QTR addendum on the digital-negatives.com site. I "borrowed" a curve for the Epson R2400 that Clay posted to this forum a while back and have been tweaking systematically from there.

My problem is, whatever I do, I can't get any tone at all in the top 35% of my step charts. I have tried adjusting the ink limits for C,M,Y,K as well as adjusting the boost_k setting. I have set the ink limits anywhere from 12 to 60 (below 12 makes the whole chart uniformly gray and washed out), tried setting boost_k anywhere from 0 to 70, but the top 35% of the step tablet is always paper white. (I've attached a typical example). I know I will have to deal with the blocked up dark tones at some point, too, but I figure I will cross that bridge when I get to it.

Can anyone give me some advice on how to tackle this problem? I have printed a dozen step charts at this point with no improvement, and I'm starting to get a bit frustrated! Thanks very much.

Dalton

 

[dalton]

Just as an update:

I printed 12 more step charts last night. (I have gotten very good at fitting 4 small charts with 4 different curves to a single page) and did manage to get tone into the top 10% of the chart. The problem is that everything above 35% or so is extremely grainy.

Additional searches in the forum led me to this post: http://www.hybridphoto.com/forums/showthread.php?p=7738
Colin seems to be having the same problem with grain above 40% or so and eventually figured out that it might be an interleaf that was blocking enough UV to cause the grain.

I am using Pictorico OHP Premium, which I am starting to think might be a problem. I was reminded of just how difficult it was to determine my base exposure time because I couldn't get to maximum black through the film. Is OHP Premium suitable for working with digital negatives & palladium? Could this be my problem?

UPDATE: I bought my OHP Premium at B&H, it is the one in the newer white packaging. I noticed that Bostick and Sullivan sell OHP Premium as well, they list it in the older package with the waterfall on the front. I am assuming this is the stuff that everyone uses and likes. Has Pictorico changed the formula? The version I have is a bit milky translucent, it is not perfectly clear.

 

[Colin Graham]

Hi Dalton,

Sorry to say this, but I'm glad it's not only me. I was beginning to think I was nuts. I've been beside myself trying to get a handle on grain. The interleaf I was using was the culprit with the UV blocking above 40%, but still the grain is an issue.

I did do some kallitypes to compare process results, and the grain is masked somewhat by the emulsion and the paper surface. But being sensitized to the grain by my issues with carbon transfers, they still stand out to me.

I've been experimenting with using just 2 dark inks- MK and Cyan and dispensing with yellow and magenta. I know yellow is a great UV blocker, but blocking UV isn't a problem- I'm down to 11 limits on the dark inks to get some tones in the 5-10 range, even with kallitypes. But like you say the tonal transition come up looking a little mushy. The magenta I've heard has next to no blocking value at all.

So far results are somewhat encouraging. Based on Ron-san's advice from the thread you referenced, I started in the 1:4 range of MK to cyan. I made step wedges of just the 0%-20% range on one sheet of pictorico and filled them with different ink strengths and arrived at a mix of 40 cyan and 10 MK. I left the K boost at 25- although I'm not sure if that even applies with the cyan set so high.

I really want to get this working because everything above 40% is just perfect. I hardly need to curve it at all, even 95-100% is just there. Its bewildering that the dither matrix is so obvious with the dark inks in QTR when the light inks are so smooth. Printing HSL steps, even colors absolutely loaded with black and yellow- dark green for example- the dithering isn't nearly as apparent in either the negatives or in the resulting contact print, it just isn't an issue. But with color negs, the sweet spot of UV blocking is mercilessly thin, and I have to use some pretty wild curves to span even a 21 step wedge. Not nearly enough separation for a full range of tones. Incidentally, I've even tried making a dark green from the dark inks in the QTR GUI, still grainy.

It makes me think (hope) there are still some finer points of the QTR setup I haven't gotten a handle on. I've tried all the dithering algorithms, paper surfaces, not sure what else to try.

My MK levels are so low in order to get detail I'm considering experimenting with PK inks next. I did notice when I first started printing these wedges out that the higher the density the less the apparent grain- wysiwyg anyway. Can't print through them to tell what the contact would look like! I've tried to tailor my emulsion contrast to accept much more exposure, but that didn't work either. With my processes, the MK ink is simply too efficient a UV blocker, especially compared to the other 7 inks. Maybe PK will be more... equitable. Anyway, wanted to share some of the things I'm trying, so at least you know you're not alone. Cheers.

 

[dalton]

Hi Colin,

Thanks for sharing your experiences. My next step was going to be to change the ratio of mK in relation to C, M & Y. The 1:4 number sounds great, I will start there and see what happens.

I should also mention that I have noticed that my Epson R2400 seems to lay down ink much heavier than some others. I remember when I was calibrating QTR for regular inkjet printing, I always had to turn the ink limit down very low to get any separation in the darkest areas of the print. This is the same thing happening in reverse (makes sense), but it is disheartening because I know I have much less control over those low numbers than I would if they fell somewhere in the middle of the range. I just don't have enough fine-tune control when my dark ink limits are all in the 10-15 range.

As you mentioned, my mid-tones look great! That's what is keeping me going at this point, looking at those delicious mid-tones and hoping that someday I will have highlights and shadows that look as good.

 

[sanking]

Colin,

I would be interested in your experiments with the PK ink in place of the MK. I am getting more grain with carbon printing than I would like and have thought of trying the PK route.

I am attaching a carbon profile for the Epson 3800. This profile produces a Dmax of about log 2.5 when printing with a fairly high relief tissue that I make. The profile started out at the Formulary with Ron but I made some pretty substantial changes to it for another tissue.

Sandy

My MK levels are so low in order to get detail I'm considering experimenting with PK inks next. I did notice when I first started printing these wedges out that the higher the density the less the apparent grain- wysiwyg anyway. Can't print through them to tell what the contact would look like! I've tried to tailor my emulsion contrast to accept much more exposure, but that didn't work either. With my processes, the MK ink is simply too efficient a UV blocker, especially compared to the other 7 inks. Maybe PK will be more... equitable. Anyway, wanted to share some of the things I'm trying, so at least you know you're not alone. Cheers.

 

[Colin Graham]

Thanks for sharing your profile Sandy. It looks very similar to the best results I could get from 4 inks, curve included. My tissues are fairly thick with a .7% pigment load (watercolors) and I'm using a 1.5% Ammonium dichro and brush sensitizing. The only difference is I've been using a 37 limit on the light inks.

The shadows and midtones look so great I'm considering just doing low-key images from here out! The answer has to in there somewhere. I was half dreaming of doing separation negs- highlights with HSL/ChartThrob and mids and shadows with QTR...but then I wake up in the gutter with a broken bottle for a pillow.

 

[Kerik]

I am not a carbon printer, but for Pd I've only ever used PK ink with QTR and I get extremely smooth tones with my current profile.

 

[sanking]

Kerik,

Have you posted your Pt/Pd profile for the 3800 somewhere? I had a copy of it from a third party but appear to have lost it.

However, what looks smooth in pt/pd on the textured type surfaces we typically use for this process may not look smooth in carbon. Carbon prints are often transferred to smooth surface final support papers. On this type of paper carbon prints have high Dmax, great surface detail, and show grain much like silver gelatin papers.

Sandy King

I am not a carbon printer, but for Pd I've only ever used PK ink with QTR and I get extremely smooth tones with my current profile.

 

[Kerik]

Sandy,

Yeah, I understand. But, I heard from one person who tried Ron-san's MK pd profile on the 3800 and got grainy Pd prints. I don't know this person's printing capability, however and I haven't tried Ron's profile myself. I have a new version of my profile which gives me a very linear step wedge print (based on Ron's method of using the scanner as a densitometer outlined in his fine article - thanks again, Ron!) It's on my other computer and will post it later tonight or tomorrow.

 

[Kerik]

OK, here's where I am. These graphs are based on eyedropper readings of scanned and leveled Pd prints of step wedges (following Ron's method). The blue line is my previous 3800 profile with no gray curve. The pink line is my profile with a curve I spent DAYS linearizing based on UV densitometer readings of negatives (I only have a transmission densitometer). Turns out a linearized neg relative to UV does not give you a linear print. Now I understand why my shadows were always too compressed... Duh.

The red line is my first crack at using Ron's method. Yesterday I made several negs with this profile with 2 workshop students and they all printed quite well. We used pure palladium, arches platine single coated and potassium oxalate at room temperature. The log UV density of the Dmax on the neg is about 2.4. This leaves just a bare hint of tone below paper white which goes away with the addition of a small amount of Na2. I could increase the neg Dmax by adding more yellow or more black boost, but for now I like it where it is.

Now that I'm understanding the whole QTR thing a lot better thanks to Ron's article, I see that I had made some strange decisions (more likely random tweaks) on some of the variables when I first made this profile almost a year ago. For example, I have Cyan off and I don't know why. But, for now, I'm so pleased with the results that I'm not going to back track and fix it. Time to make some prints.

 

[Kerik]

One small correction. COT320, not platine, but they are essentially the same paper.

 

[Colin Graham]

I starting messing around with PK today and must say I've very encouraged. I'm still trying to get more contrast in the 0-20% steps, but the light tones are definitely there, and with very very little grain! They look as smooth as the mids and shadows.

Kerik, thanks for sharing your profile for photoblack, it gave me the beans to spend another day testing... I'm sooo wanting to make some prints.

 

[Kerik]

Colin,

You're welcome. I'll be curious to hear how it works for you.

 

[dalton]

Colin: thanks for the update. Please let us know how it goes with the pK negatives. I am not excited about the idea of switching out my mK ink (I still print a fair amount ofinkjet prints on matte paper, my 2400 has never been loaded with pK ink), but at this point I am willing to try anything once to build a smooth curve and see what a nice Pd print looks like.

Regards,
Dalton

 

[Colin Graham]

Well, I'm pretty thrilled now. For anyone having QTR grain issues, PK is definitely the way to go. I'll post some scans when dry, but I'm getting wonderful gradation from highlight to midtones, no grain and no crossover artifacts from the dark to light inksets. Sweet mercy what a relief! I might actually get to print a photograph tomorrow instead of a step wedge:~}}}

PS-Dalton, sorry, forgot you weren't using a 3800. Still, I think it'll be worth a cart swap for these results.

 

[dalton]

Colin, did you have to modify your curves significantly when you switched inks? Or do mK and pK have roughly the same blocking power on transparency?

 

[Colin Graham]

Well, I think I'm ending up with about a 15 limit for PK, cyan and magenta, 10 yellow and a 35K boost. I started off considerably higher, around 30 for black with a 50k boost, 15 for Y-C-M then went much too low, but after a few tries got to were I am. It really surprised me how little photoblack I needed. The contact is fairly wet still, but it looks quite nice. I haven't gotten to sampling for any curves yet, but the steps appear very orderly and linear. I also used a 23K, 15 Cyan (no magenta),5 Yellow with a 32 K boost and got very similar results, possibly a little better.

The limits seem in line with what others are using for MK, so I'm wondering if my process is just unusual... or maybe Epson did a 'quiet' modification to their inks? But at this point, I'm just happy to get results.

 

[sanking]

Colin,

Please attach a carbn profile with the PK inks when you are satisfied that you have done about as well as possible. I am very interested in trying this myself as grain is definitely a problem with the MK inks in carbon. I just spent about a week testing various permutations, and a pad of Pictorico, but I am sure that the grain could be better as it is more more noticeable with the Pictorico negatives than with a continuous tone step wedge.

Don't rush on my account to put it up, however, as I won't be able to do any more testing until next week. I am actually in Louisiana today heading for Santa Fe and a carbon symposium this weekend at Bostick & Sullivan.

Sandy

Well, I think I'm ending up with about a 15 limit for PK, cyan and magenta, 10 yellow and a 35K boost. I started off considerably higher, around 30 for black with a 50k boost, 15 for Y-C-M then went much too low, but after a few tries got to were I am. It really surprised me how little photoblack I needed. The contact is fairly wet still, but it looks quite nice. I haven't gotten to sampling for any curves yet, but the steps appear very orderly and linear. I also used a 23K, 15 Cyan (no magenta),5 Yellow with a 32 K boost and got very similar results, possibly a little better.

The limits seem in line with what others are using for MK, so I'm wondering if my process is just unusual... or maybe Epson did a 'quiet' modification to their inks? But at this point, I'm just happy to get results.

 

[dalton]

Colin,

You are my hero. Switching from mK to pK ink completely solved my problem, the tones in the top 30% are now perfectly smooth. I still have to work on the linearity of my curves, but that is not daunting at all now that I have a nice smooth step chart to work from. A thousand thanks!

Dalton

 

[Colin Graham]

Great! Glad it worked for you too Dalton. Praise be to Kerik, I was so demoralized from failed tests I don't know how long it would have taken me to start experimenting with it had he not mentioned he'd been using PK all along.

Sandy, I've got some curves worked out but I'm waiting for some paper to show up to test it. I'll post my results as soon as possible... I wish I could have made it to the Symposium, sounds like a great event. Seeing some of your prints in person would be worth the drive.

 

[dalton]

Yes, I owe Kerik a big thanks too! My step chart dried overnight and I have had a better look at it in the morning light. The tonality is fantastic. Now I'm ready to linearize and get to printing some actual photographs. I was starting to get a bit desperate there, but now that I know I have a workable solution I am energized again.

I got a chance to visit both Colin's website and Kerik's website, both have some excellent work. It's great to find a forum where people are making great photographs and sharing information like this. Thanks again.

Dalton

 

[Colin Graham]

Hey, many thanks Dalton. I spent a little time at your site too. Great layout, and I really like the Everything I thought I knew gallery. Ahem, might have to pirate some of your code!

I'm still tweaking the carbon (switched papers mid-testing, oof) but I got a good PK profile for PD-toned kallitypes. Arches HP paper in a 5% citric acid prebath. I tried it in both a 20% sodium citrate developer (+ 1ml/liter of 5% K dichromate to help clearing) and 7.5% sodium acetate+ 3g tartaric acid/liter. Haven't tried in potassium oxalate yet. Maybe a little specific, but perhaps someone will fancy having a go with it.

I tried it in Lanaquarelle, but was fairly grainy and soft as is. I'd like to try it with an acid prebath next.

Man, QTR can absolutely glow when everything is firing right. Thanks again to Ron-san for all the generosity and help and Kerik for the solid nudge in the right direction!

 

[Colin Graham]

Here's a PK carbon profile, though again the caveats are considerable. This working with a 1mm tissue thickness of .7% M Graham lampblack, a 1.5% sensitizer and exposed with a bank of F20 T12 bl bulbs with about 90mm clearance on new Pictorico for 17 minutes.

I did find I can bump the contrast curve in Ps and make this work with more dilute pigments and thicker tissues, etc, so it may be a good start for someone.