There are two options for your negatives – actual film or digital negatives. There is a lot to be said for actual negatives but as I haven’t taken too many black and white photographs in 10×8 I thought it best to start with digital negatives (it gives you more control as well).
Although I’ve gone through some of these stages already I thought I’d start again as I’m now using some slightly different chemicals and processes. It’s also good to rerun some of these things once you’ve learned the basics (and I think it’s a process that you end up going through again and again as you try out different papers, chemistry, treatments, humidity, etc., etc).
One of the big advantages of the digital negative process is that you can come up with a working methodology and then stick to it, making any changes to the final result by changing your image in Photoshop. The main downside of this is that you have to calibrate the system somehow.
This calibration process typically has two steps.
- Work out what your base exposure needs to be
- Work out a curve that will be used to create a smooth linear progression from blacks to whites.
This is probably the easiest step, particularly if you have a Stouffer step wedge.
If you make an exposure quite a bit longer than you would expect. Let’s say a 30 minute exposure to begin with but this sort of depends on how strong your UV light source is. Then you can use the result of this to work out an exposure that just gives you full black where your negative is clear. Here’s a diagram showing how to make a test exposure.
First of all you can see that we use a sample of the OHP film that we’re going to use to make sure we include that in our equations (after all it blocks a fair bit of UV light). We then check the end result to find out which step creates a full black. If the full black occurs at a step that shows -1 stop then we know our exposure should be 30/2 = 15 minutes. Here’s my step wedge.
Types of Digital Negative
There are three main types of digital negative you can make.
- native inks and native driver.
- native inks but dedicated software
- custom inks with dedicated software
Native Inks and Native Driver
The goal of this method is to find the colour and tone that block UV the most. To do this you can print out a spectrum of colour and tones, make a negative out of it and then a UV print and look for the area that is lightest. This is the system that most people will use.
Native Inks and Custom Driver
Custom printer drivers have been written that let you mix your own sets of inks together. In order to do this, you make a step wedge of each printer colour and do some (arcane) magic and then you have a fancy preset that performs very well. The advantage of this is that because the system can use multiple overlaid ink colours, the dithering should be better. A good example of this, and the most used I think, is Quadtone RIP.
Custom Inks and Custom Driver
Finally, we have the piece de resistance. Using a set of dilutions of carbon (possibly with coatings to help it work in an inkjet nozzle) and a custom software application (QuadtoneRIP for instance). The two examples I know of are the Eboni-6 system and the Piezography system
I hopefully will end up with the final system but for our first tutorials we’ll cover the first two systems.
In the next article we’ll take a look at establishing your base exposure