How to make a negative

Negatives have to do two things, be black enough to stop light whilst being clear enough to let light through easily and have the correct resolution to deliver your image onto the printing plate.

You can measure the blackness of a negative using a densitomiter, which is a machine with a light one one side and a photocell on the other. The negative is placed between the two and the amount of light the cell sees through the blackness of the negative is given as a number (eg DMax 2.5), the lower the number the more light transmitted and the worse the negative. You should ideally have a DMax of over 3.0, but if the light source in the exposure unit is low in intensity then you can get away with a DMax down to 1.8, which we have found is the minimum usable.

The clear parts must let as much light through as possible, photographic and laser negatives let a lot through giving a DMax of typically 0.05, whereas inkjet negatives have a white opacity and a DMax of around 0.35 to 0.5. This means you need to shine more light through the negative and lengthen your main exposure time.

How dark black your negative depends upon the light intensity and the duration of exposure. Higher intensity lights require darker negatives. If you reduce the light intensity you can make good plates using less dark negatives, but if you want to make great plates and not have any issue over negative opacity then obtain a DMax of over 3.3.

You can make negatives using these methods;

          Photographic negatives- using an imagesetter and photographic film- it was the conventional way negatives used to be made, but is now very outdated as it uses expensive silver halide to give opacity instead of cheaper carbon. Requires developing and fixative solutions and an, expensive to maintain, machine. Not recommended.

          Laser ablation- requires a laser and special carbon coated film. The laser selectively removes the parts that light is to be transmitted through. Very expensive machines that are slow to use and a hard to get consumable available from only a few manufacturers make this an expensive and potentially problematic solution.

Daylight AQ film- 15 years ago this was an excellent replacement to photographic film, but direct printing has replaced it for convenience and cost. The user uses a laser printer to print a positive on vellum (frosty polyester film) then sandwiching the AQ film between it and the light source the parts that are clear set the film and the parts covered by toner can be removed using a spray and water.

Laser printed film- The best solution for producing low cost resilient negatives. Only some laser printers will work, we recommend Hp as the easiest to enhance. To produce a negative from a laser printer you need to do three things, adjust the toner settings to increase the toner dropped down (you will using find this in the print properties accessed through the control panel), use the correct film, imageblack laser film is an optimised polyester film with a calendared surface suitable for receiving toner (if you use the wrong film it will simply not allow enough toner to stick to it) and you must enhance the output using heat and solvent. You can enhance negatives using toner density spray (available in most countries in aerosol form) or by wiping with solvent and heating. The exact type of the solvent depends upon the type of printer, we recommend white spirit (turpentine or Stoddards solvent) for Hp laser output. Wipe quickly with a lint free cloth and heat with hot air gun. We can recommend other solvents that will be more effective than white spirit, even so that they don’t require heating, but you have apply them non-aggressively otherwise you will remove the toner. Keep the film dry and free from dust otherwise you will get white spots on the negative.

Inkjet printed negatives- this is the easiest method to make, the lowest cost and will deliver very high quality, very dark black negatives using all inkjet printers. The drawbacks are that the ink will be expensive (unless you install a continuous supply system) and the negative will be susceptible to be scratched and damaged by water. But for a negative that is used only a handful times it is an excellent solution. Although we have never failed to make a negative on any inkjet printer- not all printers are easy to make negatives on or deliver particularly black negatives.  The worst generally are Brother, Lexmark and Epson, but it depends on the model itself not the manufacturer. The best, as with laser, is Hp. We would recommend any Hp inkjet, but if you just want a negative printer then use the lowest cost or the basic PSC (printer copier scanner) type as this will provide slightly higher resolution. To make a negative you will need to do the following, adjust the ink volume to maximise the amount dropped, with Hp models this can often be done by selecting ‘Presentation Printing’ or ‘Specialty Paper’ from the shortcut menu and you will have to use imageblack injet film or similar. imageblack film is a heavily optimised coating on polyester that is very ink receptive and will make the black very opaque, typically OHP film will either not work at all or be very grey from the holes present.