Densitometry & Platinum Print Editioning
March 22, 2012
The use of densitometry in the creation of platinum prints is important if a printer wishes to create consistent and repeatable results in the darkroom. Part of the charm of the platinum print is the fact that no two prints are exactly the same, however if one is editioning densitometry plays a vital role in keeping each print as close as is possible to the reference print or BAT.
For every proof print I create when editioning I include a detailed step wedge, at my own studio we usually work at half size first and then go up to the final size. If you were to measure the step wedge of the proof print below with a densitometer it would show a liner response within 1% to 3%.
Densitometry is not the be all and end all of fine platinum printing, you maybe achieving accurate readings when measuring the printed step wedge on a densitometer however the print may not ‘sing’ and look too clinical. This is where experience and intuition plays a role in then fine tuning the print to achive the desired result.
The key values of a densitometer that I read are DMax and DMin which refer to the maximum and minimum density that can be recorded on a light senstive material, in this case the printing paper. Dmax varies from paper to paper and ranges from 1.3 to 1.6 for single layered prints (upto 1.8 with multilayered). In my experience papers that have been acidified before coating achieve the highest Dmax ratings. Below shows a dmax reading of 1.52
On each step wedge there is a scale from 0 to 100%, these values are used to take dot percentage measurements. If you take a reflective reading from the actual print this should be accurate to within 1-3%. The print below shows a dot percentage reading of 40% which corresponds with 40% on the printed step wedge.
I am often asked where one can obtain a densitometer and how much they cost. The price of a new model can vary from £600 to £2000+ depending on the type of functions you require. Second hand models can be had for considerably less however it is important to check how accurate the model is before purchasing. Every day I measure my meter to a reference reflection tablet that includes a white and black reference spot. When measuring the white spot it should read 0 and black spot value should correspond to the (V) value on the reference table, in this case it is 1.33 as is shown below. If this is not accurate it should be sent back to the manufacturer for re-calibration. I have had many different models over the years however have settled with a black and white reflection model as this is all I require.