Making 'Lith' negatives for photopolymer etc.

In another post I wrote about using photopolymer material to make printing plates.  Unlike inkjet printers, the letterpress method uses just one colour of ink to make the image. The printing block image therefore needs to be ‘1-bit’ = that is pure black or white.
Traditional printmaking uses Lithography (or ‘lith’) film which is super-contrast. Properly processed it’s either totally clear or dense black, with no mid tones.  Lith or ‘line’ films are still available and used to make images from larger or smaller artwork by photographing them in a copy camera. These huge beasts (sometimes the size of a room) were made so very large negatives could be made optically.  Most printers make their negs digitally now.

Part of the interest in this process is making photographic images which look different from the usual darkroom or inkjet prints. Reducing a picture to just black and white changes it radically, and some judgement is needed to get images which work well. 

A great example is right here on my coffee mug:

It’s a lith rendition of the famous Alberto Korda photo of Che Guevara. The original was shot on 35mm and continuous tone -i.e. with shades of grey:

This graphic rendition is relatively easy. Everything lighter than a middle grey becomes white, everything darker than the mid point goes black. Just moving the levels sliders around will achieve something pretty similar if you're lucky but there’s a better and more controllable way.

Workflow in Photoshop.

Choose a bold, graphic image that you think will work well and be recognisable at small size since the first test plates at least are likely to be small. Here, as so often(!) I’ve chosen a picture of Algernon.

Open the image in Photoshop and convert it to black and white. Use Image>Black and White to do this as you can tweak the colour conversion to control how the contrast goes. Here I’ve boosted the yellows but reduced the reds so the difference between his lighter and darker stripes stands out more.

tweaking the colour responses in the B&W converter to get good contrast.

You can also selectively lighten or darken areas of the image to help them go towards black or white as desired. Here I’ve used the burn tool to deepen the shadow under his chin and his pink nose, (cute though it is) needs to be darkened so it goes black not white.

Now choose Image > Adjustments > Threshold

The image goes full ‘all or nothing’ black and white. The slider controls the threshold value- the point where the tones are split. By default it’s in the middle of the range but pulling it left or right allows fine tweaking of how the image reads. 

Threshold level 103.  Too light...

Moved up to 128.  Much better.

- but further up to 149 is too dark.

The key is to find the best point to give a recognisable image, in this case a good stripy face and not a black or white blob.  If you can't get the detail you need everywhere, cancel Threshold, go back to the continuous tone image and dodge or burn the problem areas to bring them in range. 

Now all that remains is to Invert (cmd-I) the tones to make a negative and print out onto inkjet film. I use a pretty crude laser printer and cheap photocopier acetate as it gives a good dense black.

I'm not Algy - I'm his evil twin...

Note that you DON'T need to flip the image as it will be exposed 'emulsion-to-emulsion' and this will automatically produce the reversed printing plate you need.

Another thing I've found useful is to have a thick black border around the final negative when you print it. - Just choose Image>Canvas size and increase both width and height by 10mm or so.  This means there will be no unwanted edge lines near the image which would need trimming off before printing.

Dot screens for half -tones

It’s possible to get more tones (shades of grey) with letterpress by using dot screens. The image is still only made of black ink and white paper but a fine pattern of dots gives the impression of more intermediate tones. Here's a plate for a newspaper photograph I have in my collection:

Newspaper photo printing block. The original is about 5in x 7in

It's a metal plate mounted on a wood block (see the article on letterpress printing for discussion of the depth of the block). Close examination of the surface shows it's got a dot screen:

At a normal viewing distance, the dots are almost invisible but the effect is of more continuous tones. This method is used in more or less complex forms in most commercial printing. 

Cheap, soft paper like newsprint absorbs a lot of ink so a coarse screen is needed: around 85 lines per inch is common and the screen isn't too hard to see.  High-end art books may use high quality coated stock which allows a much finer (200 lpi or more) screen which cannot be seen with the naked eye. This is, of course similar to the way inkjet print resolutions work: posher papers can exploit finer detail while 'plain' paper cannot resolve as many dots per inch.

Personally, I don't like the dotscreen 'look' and prefer to use other processes (like the darkroom!) for mid tones in prints. However, if you do, here's how to do it in Photoshop:

Open your image and if it's not already black and white, convert it:

You'll need to boost the contrast quite a bit higher than you would normally. Something like this:

Next choose Filter>Pixelate> Colour Halftone.

The Max. Radius number will control the coarseness of the screen. Small numbers give a fine screen, larger ones make the dots bigger and more obvious. Here it's set to a fine 5 radius.
Set all the channels to 45 degrees for the classic dot screen effect (or vary it if you like of course):

For comparison here are some different dot radii. - Not easy to see on a web page  so I've exaggerated the effect by using a wide range of numbers.

Dot Radius = 5

Dot Radius = 20

Dot Radius = 30

On the finer screens, the dot pattern is still there and effectively made from  pure black circles of different sizes. Here's a closeup of the 5 radius:

Detail:  Dot Radius = 5

The image on your computer screen is of course made up of another grid of dots- the screen pixels so print out test samples on paper to see just how it looks. Once you're happy, don't forget to invert the tones to make a neg and load up the transparency material..

Photopolymer - Letterpress printing of photographs

Photopolymer is a very interesting material: A thick plastic sheet which is partly soluble in water.  Exposure to UV light causes the polymer plastic to harden and become insoluble.

It’s used to make printing plates for letterpress and other ink printing processes.
A negative is contact-exposed onto the polymer. Clear areas are exposed to UV and harden, black (on the neg) areas receive no light and stay soft. 
‘Development’ consists of rinsing the material in cold water. The soft unexposed areas dissolve, leaving the harder exposed parts in relief. The difference is small (0.1mm or so) but it's enough to make a very detailed printing plate.

Testing:

The material is Toyobo KF152.  It's relatively expensive for full sheets but the nice people at Lyme Bay Press (https://main.lymebaypress.co.uk) sell packs of assorted offcuts for around £27. This gives an ample supply of pieces for testing and making small plates. It can be cut with strong scissors or a craft knife.

* (There is also a KF95 - a thinner material said to be just as effective, if not better on thin papers. I chose the 152 purely because it was in stock at the time!) 

As it’s UV sensitive it’s supplied in a black plastic bag but can be handled in low tungsten lighting - much like cyanotype or argyrotype materials in fact. It’s an amber colour, with a slightly odd (but not offensive) smell and can be cut with strong scissors or a craft knife. There’s a protective film on the emulsion side and a harder plastic backing.

The manufacturers recommend using a Stouffer gauge (a graduated step wedge negative) and it does work but in practice I think photographers will find it easier to make an actual test negative on the printer and use that. 

Lith negatives

Negatives for this process can be made with ‘lith’ or ’line film’ which are very high contrast materials with essentially a black and a white, but no mid tones at all. This is the traditional method but digital negs are easier to make for most people! I’ll describe the process in detail elsewhere.  I used a laser printer and cheap transparency material.  

It can be confusing to work out the full process (dense areas of the neg stop the light so the material will remain soft and dissolve, reducing height and so not retaining printing ink. clear areas allow light through to harden the polymer and producing an inked area) so for my very first tests I made a dual image with both positive and negative versions!  

For the record, you need to make a NEGATIVE (tones inverted) image on the transparency material.

Simple exposure tests.

For an experienced darkroom printer this is a curiously counterintuitive process. Slight underexposure results in more apparent relief between shadow and highlights but overexposure makes a plate which looks 'thin' and without contrast.  These test pieces are tiny little images only about 15- 20mm high as this scale is easiest to set up and test in a printing press or as a hand stamp.  Large (up to A3) images can be made but apart from the expense they are trickier to get right with press setup etc.

It’s not really possible to gauge which plate would print best by eye (though I’m sure experienced photopolymer printers can do it) so I made a range of test pieces: This photo of Algernon in both positive and negative at various exposures, plus this set of nine identical letter Ps which I exposed as test strips: 100 -900 seconds and then 900 - 1700 seconds. This stuff needs a LOT of exposure! 

More about exposure testing below.

Post-exposure.

Once the photopolymer has been exposed it’s rinsed in cool (less than 23 deg.C) water for 2-5 minutes. A soft brush is recommended to help remove the soluble polymer (I used an eyeliner brush which has very fine bristles like a paintbrush but with more stiffness so there’s a gentle scrubbing effect). Too much rinsing can damage the surface so rinse just long enough until the milky-looking and slimy-feeling soft stuff is gone.  The plate is then dried thoroughly and then re-exposed for 1.5 to 2 times the original exposure. This hardens the remaining polymer material completely, making it durable and ready for printing.

Exposed plate before washing out.  A faint image is visible already.

Washing in running water dissolves the unexposed areas and 'develops' the plate.

Washed out to reveal the relief pattern of the image. This must be dried, then re-exposed to ensure it's fully hardened.

Adventures in letterpress.

I’m lucky to have inherited my grandfather’s 1930s  ADANA 6”x4” printing press. These little machines were made to print with metal type onto paper in the true letterpress method. It’s an awful long time since I did any traditional printing like this so I’m re-learning it all but enjoying the process. The advantage of a ‘proper’ press is that everything from the amount of ink applied to the pressure is very controllable. It is possible to use this stuff in a simple screw press or even as a hand stamp but the results will be more variable.

Adana 6"x4" letterpress machine. A wonderfully mechanical device in the clutter of the workshop

Type height.

British printing presses use a standard type height of 0.918 inch (23.32mm). Any printing block needs to be exactly this thickness to work properly. The KF152 photopolymer is 1.52mm thick so it needs mounting to a block (usually of wood) to raise it ‘type high’. This height is crucial: Printers will paste thin pieces of paper to the back of blocks to adjust the height until it’s perfect. The ink rollers are set to deliver precisely the right amount based on this size: any lower and the print will be pale und under-inked, higher and too much is applied, leading to rough, blurry edges and loss of detail. I took some time with my block for the test pieces to get it right.

All type should be exactly the same height. 0.918 inch

The block is put into a frame (called a ‘chase’) along with any other type needed for the design and then packed out with ‘furniture’: pieces of metal or wood before locking it in place with expanding blocks called ‘quoins’. Once everything is assembled on a flat surface it’s called a ‘forme’. 

The forme goes into the press bed, the rollers transfer ink from the disk at the top to the printing surface and then it’s ready for the paper. Everything is very accurately controlled so results are consistent. All this means I could test the differently exposed blocks side by side for comparison.

Photopolymer plate installed on wooden base and inked up.

The best print from the test plates described above.

-and the test strips. Exposure times go from 100 seconds (top left and invisible!) to 1700 seconds (bottom right)

1200 seconds (20 minutes!) exposure seems to give the best detail with neither fine lines too faint or darker areas spreading out.  This is quite a long time by traditional alternative process standards - I reckon on about 6 -12 minutes being plenty for cyanotypes with this unit but it's fine. I could use another more intense UV source but it's easy to use my standard exposure box.

These are my very first forays into this technique so I know they aren't very good.  Once I've got more experience, and learned more I'll write another article. If you have used it already, please get in touch and share your expertise!

 As promised I've written another article on the neg making process. Making a pure black and white image with no mid tones is an interesting exercise in itself. Find it here: 

http://oldphotoprocess.blogspot.com/2021/12/making-lith-negatives-for-photopolymer.html

Cyanotype and Argyrotype paper testing

I'm making a set of sample prints for UCA at the moment; They want examples of alternative processes for use on open days etc. so I'm taking the opportunity to do a bit of testing while I'm at it.   Many practitioners recommend certain papers and the differences can be quite marked.  Recommendations are interesting but also frustrating at times. Talbot apparently favoured 'Whatman's Turkey Mill' writing paper for his calotypes but this is long-defunct and nobody seems exactly sure what was the magic quality it possessed!

lots of test pieces - all A3 size.

Finding papers

Like Talbot, many guides to process emotion papers which turn out to be either unavailable or ultra-expensive.  Here I won't be extolling the virtues of 'Buggins' patent Premium Heliofibre' (which, as I'm sure you know is hand-made by Tibetan monks under moonlight and washed in unicorn's tears) or the like. - Just stuff readily available in the UK. All the papers below are available either from specialists like Silverprint or decent-sized art shops. (although I'm not sure about the sketch pad stuff!)

Papers tested.

Seawhite Watercolour Acid-free 350gsm 

Fabriano Aquarello Watercolour (25% cotton) cold pressed 300gsm /140lbs 

Arches Aquarelle Watercolour cold pressed 300gsm /140lbs 

Daler Rowney Aquafine smooth hot pressed Watercolour (100% cellulose) 300gsm /140lbs 

Victor Stationery Sketch Pad paper (no specs but much thinner and lighter than the others here. - I bought a big bundle of it in a charity shop for very little money) 

Arches Platine hot pressed 310gsm 

If you're not familiar with paper terminology, 'gsm' is grammes per square metre. and the heavier the weight the thicker the paper stock. 'lbs' is a bit more complicated as it refers to the weight of a ream (500 sheets) of a given paper in its 'basis size' - but again, more weight = thicker stock.  'Cold pressed' papers have a rougher, more textured surface than 'hot pressed'.  'Watercolour' in a title is generally a good thing as it means a paper will absorb liquids well and generally stand up to rinsing etc. without falling apart. 'Acid free' and papers with lots of cotton fibres are also (usually) desirable qualities.  All of this said, test whatever you have: Sometimes a cheap, unimpressive paper can yield great results. - which is why I buy stuff like the sketch pads above.- you never know!

Consistency is key

For these tests I used the same batch of sensitiser, coating technique, drying method, exposure time and processing. The negative has a very full range so any differences should be apparent.  For the record the processing sequences were:

Cyanotype: A: 25g Ferric Ammoniun Citrate per 100ml distilled water.  B: 10g Potassium Ferricyanide per 100ml distilled water. Brush coated* and air dried overnight. Exposure: 11min in my LED UV box, 1min rinse in distilled water, 5 min rinse in running tap water, 30 sec in Hydrogen Peroxide bath (1%) then 1 min post-rinse in running tap water.                                                                                                         *I made both single and double-coated test sheets for everything.

Argyrotype: Fotospeed pre-mixed sensitiser. 5ml per 12"x16" sheet, rod coated and air dried overnight. Exposure: 5 min in the UV box. 5min rinse in distilled water,  3min fix in 7% sodium thiosulphate solution (made with distilled water) 30 min rinse in running tap water.

Cyanotype results

The prints were remarkably similar.  Despite brush coating, which means it's not easy to ensure consistent coverage there wasn't much to choose between the finished prints. 

As expected, the very thin 'Sketch Pad' stock was the worst, with a weak, patchy tone and limited tonal depth Its also horrible to work with, cockling and buckling when coating, very floppy and fragile to process and about as flat as a poppadum when dried! It may be ideal for some process but not these!

'Sketch Pad' paper

  

The Arches Platine was hard to rinse clean, with a distinct yellow tone to the highlights. - This will eventually darken to blue-grey as it's residual toner in the fibres.  Longer washing might clear it but that could reduce the blue tone too. Double coating increased the depth of colour but only by a small amount, and the yellow highlights were twice as bad. Arches Platine was specifically developed for platinum and palladium printing and its been the default alt. process paper at specialists like Silverprint for a long time, but it's not the best for cyanotype.  

Arches Platine

Daler-Rowney Aquafine was better, giving a good, strong blue -or deep blue-black if double coated and nice clean whites. Its cheap if bought in big, thick pads of 50 sheets and easy to use. The surface is quite smooth- almost bland but if this was a consumer review I'd mark it as 'best value'. Ideal for learning and experimenting. 

Daler Rowney Aquafine

The Arches Watercolour managed a slightly better colour, but like its 'Platine' cousin it showed a yellowing in the highlights. - This wasn't a strong as with Platine but it's there and, annoyingly only really visible when fully dried. - They looked fine in the darkroom wash! 

Arches 300gsm watercolour

Next is the Fabriano Aquarello which produces a lovely deep tone, especially when double coated. There may be just a hint of yellowing. - (I might try 5 min in the distilled water wash plus 5 min in tap water) but it's good stuff.  

Fabriano 300gsm watercolour paper

Finally the Seawhite 350gsm watercolour paper.  This is the thickest paper and has, I think absorbed more sensitiser. Not only is the tone lovely and rich, with a great blue-black colour in the shadows (again, double coating is marginally better than single coating) but the overall image looks darker. The tone separation is the best (see the dark area in the centre of the image) and the texture is pleasing. The texture is more pronounced on one side of the paper so you can choose between two surfaces in one sheet. - definitely my favourite and happily, not the most expensive!

Seawhite 350gsm watercolour paper

(by the way, the image I chose is an iPhone picture of raindrops on the roof of my car, printed as a 10.5 in x 15in digital negative. It's quite contrasty -if anything, a bit strong. Something with more subtle mid-tones might have been more appropriate))

Argyrotype results.

This is a trickier process and as the sensitiser is quite pricey and harder to coat evenly I used the glass rod technique, putting a measured amount (5ml) onto each A3 sheet. Double coating is possible but I find it tends to reduce overall contrast without contributing much to the maximum density. It 'dries down' a LOT- about 1 stop/zone according to the instructions but most of the darkening takes place in the shadows. Negs for Argyrotype need quite a bit of boosting in the shadow areas (if making digital negs apply a curve to give your neg more density and contrast in the shadow areas - I'm doing some experiments on this but keep getting sidetracked by other work!). Careful tests are important to get the best from each paper but I went for a standard 'average' time of 300 sec (5 minutes) exposure for every print.

(My test image this time was my 'Open Door' (after Talbot) picture. Made on a DSLR and printed as a 10in x 14in digital negative).  My correction curve is quite crude but now I've found the most promising paper stock, hopefully I can get back to the curve tests soon. 

the 'Open Door' setup...

Again, the 'sketch pad' stock was pretty dreadful: misbehaving physically (floppy and fragile when wet, curly and pine to creasing when dry) and with the weakest tone. It just can't absorb enough sensitiser:

'Sketchpad' stock. - it actually looks better on the screen than in reality!

Next was the Daler Rowney paper. This didn't do nearly as well as it had for cyanotypes. The tone is blotchy and pale..

Daler Rowney 300gsm watercolour paper

Next was the Arches 300gsm. I really want this paper to be great at something as the pads are so beautiful! However, it's not the best for Argyrotype. There's a 'veiling' effect which isn't as bad as the Daler Rowney but it weakens the shadows.

Arches 300gsm watercolour paper

The Arches Platine is much better, albeit colder in tone:

Arches Platine paper

Seawhite 350gsm is good, with a much better tone and shadow density.

Seawhite 350gsm

Fabriano 300gsm  has the edge though. The blacks are noticeably deeper than any of the other papers and while it's a bit over-contrasty, this should be easy to solve with a bit of negative curve adjustment ( I really have to do those tests now!)

Fabriano 300gsm watercolour paper

So if you're the type of person who skips straight to the end for the verdict on what to buy, I'd say Fabriano 300 for Argyrotype (interestingly they supply "Fabriano 5" paper in the Fotospeed kits) and Seawhite 350gsm for cyanotypes. 

As Argyrotype sensitiser is expensive, it doesn't make much sense economising on paper while learning the process, but if you're on a tight budget or making lots of prints, the Daler Rowney paper is excellent for the price.

As you can see (I hope!) from the pictures there's quite a difference in colour with Argyrotype on different papers, so that may also be a factor.  If you have a favourite paper not mentioned here I'd love to hear about it. - Please share your results and experiments. - Its what we're here for!  - Peter Renn

UCA Collodion workshops 2021 - worth the wait!

 Lots of wetplate workshops for UCA this year: As well as the usual sessions I was very happy to keep my promise to those people who were all set in 2020 only for Covid to force us to cancel.  Finally in June 2021 we got to catch up. 

Lots of images to display:

Maria Romero Blasco.  The mask will serve to date this image in future!

Reeve Hart.

Victoria Cooper Pedrote.  

These two really show the versatility of collodion: The left hand one is anly about a stop less exposure than the one on the right, which while technically ovexposed has a wonderful Julia Margaret Cameron feel. - I love them both!

Florentina.  Talking of Cameron, she too was photographed holding one of her favourite lenses and was fond of a patterned shawl.

 

Kerry Holland.  Working the props to great effect.

Charlotte Hawthorn.

Monica Yang.  Keeping it simple...

Avi Rehill.   going for full effect.

Alex Barker. 

- that's Jakob Winterborne under the mask

- while Josh Lieseke brought his full orangutan costume. 

Heather Tonkin doing different looks.

Olivia Cooper.

Priyanka Pattni.  She brought the full 'Indian Princess' costume - to great applause.

Xu Ma.  We were deliberately trying to do incomplete developer pours for edge effects. - much harder to do than you'd think!

Taylor Harbison.  Some nice developer-induced edge effects on the left hand one.

Hayden Wilde has assisted several times now.  Nice to make a 2021 portrait to go with the earlier ones.

Taylor Harbison.  An ambrotype (ie on glass not metal) and deliberately over-exposed to solarise parts of the face and hands.

Izzy Sherlock-Fuidge.  Another nice simple portrait.

The Lieseke-Harbison expedition: Believed lost in the jungle for years, when discovered the explorers were in a terrible state... ;-)

Dan Holden.

Chris Reinstadler.  The camera and bench can be seen reflected in the glasses.

Toni Castle.  I've learned that UV-reflective coatings on glasses are good for your eyes but appear extra-shiny on collodion.  

Dan and Izzy exploiting the long (30 second) exposure times by moving deliberately...

Thanks to everyone who took part. - We had a lot of fun and made some wonderful, skilful, experimental, funny and beautiful pictures. - The creativity and the love of photography shines through. - Well done!

If you'd like to go on the mailing list for alerts on posts to this blog or maybe even to contribute articles, send me an email at my UCA email address. - Peter.