Shortly after I got my first 35 mm camera many years ago I also put together an inexpensive black & white darkroom to process my photographs into printed images. The black & white prints I could make myself were far superior to any local printing that was available to me.
Fast forward to the present digital age. While commercial printing results are greatly improved I still prefer to make my own small prints and notecards but now on an inkjet printer. A couple of years ago Canon had a rebate program on their PRO-100 printer that enticed me into upgrading to a midline photo printer. This printer has a 13 inch carriage and and 8 tank ink set. With the rebate the cost of the printer hardware was that same as the cost of one set of ink tanks.
It didn’t take long for me to start to wonder about the ink costs. Since I rarely print color images I have to consider the cost of the color ink that is used just to keep the print head clean. One evening I ran across a methodology for estimating ink usage on the Red River Paper web site. I have adapted it to estimate the ink usage for my favored print, a 6” x 9” warm-toned black & white image with an identity plate printed on 8.5” x 11” Canon Pro Luster paper.
The Canon Pro-100 shows the approximate ink levels qualitatively in the form of horizontal bar graph. We can quantify those levels by measuring the length of the bars and comparing those lengths to the full bar. This is an admittedly imprecise measurement of a known approximate indicator of ink level in each tank. The result has some unknown amount of error but is better than nothing. By evaluating the ink usage over a relatively large number of similar prints we can distribute the estimation error over all of the prints. Red River Paper printed 200 prints. I printed 51.
We begin by displaying the ink supply levels graphic for the printer at the beginning of the session. I generally take a windowed screen shot for my records and then enlarge it on the screen to make it easier to measure. I use the millimeter scale of a clear plastic ruler to first measure the length of the full bar and then the lengths of each colored bar. The actual sizes and units don’t matter because we are using the ratios of the measurements.
Calculate the ratio (or percentage) of the colored length to the full length for each color.
Now print a few tens of prints in similar format. These don’t have to done all at the same time and I usually include a test print at the beginning of each run to ensure that the head is not clogged. Keep track of the number of image prints. The test prints and any head cleaning can be noted but both are part of the printing process so are not included in the number of prints being made. Also be certain to keep track of any tanks that were replaced during the session.
After all of the prints have been made, display the printer ink supply levels again, measure the lengths of the bars again, and calculate the tank percentages remaining. In this example you will notice that the PC, Y, and GY tanks indicate more ink in their tanks than when we started. Those three colors required tank replacement during the session.
Levels at the end of the session:
Now we can determine the equivalent number of ink cartridges used by subtracting the levels at the end from the levels at the start for each color and adding the number of tanks replaced.
We can now just add up the fractional tanks used to get the equivalent number of tanks used during the session, in this case 2.48 tanks. Multiply that value by the cost/tank, $15.63, to get the total cost of the ink used during the session. Divide that cost by the number of prints printed, 51, to get an ink cost per print of $0.76.
Remember that this estimate is only valid for the particular print I was making, a 6” x 9” warm-toned black & white image with an identity plate printed on 8.5” x 11” Canon Pro Luster paper. The full printing session was also divided into two runs of 18 and 33 prints several days apart. Many small and intermittent runs may increase the ink usage required by the print head cleaning.
The ink usage by tank can be normalized or scaled by the smallest value, in this example, 0.1. Then we can see that for every one tank of M and C, we use two PC and Y, three PM, four BK, five GY, and a whopping seven tanks of LGY. I had been buying the full set of ink each time; at the time I did this analysis I had three boxes open. When I looked in the oldest box there were only two cartridges in it, C and M. Now my ink purchases are informed by my usage so I order extra BK, GY, and LGY.
The Canon Pro Luster paper is roughly $0.35 per sheet so the ink makes up roughly 2/3 of the total cost/print.