The Original is Not Always Right - Lab Prints

Printing an image can introduce a range of issues that may adversely affect the result. In the case of a traditional RA-4 print, the chemistry needs to be within specifications. A good lab will run a variety of tests, on a regular basis, to check the condition of the processing solutions.

One such test involves running a control strip: a piece of photographic paper pre-exposed with a series of color patches (black, grey, white, cyan, magenta and yellow). Once processed the test strip is passed through a densitometer that reads the color density for each of the patches. The information is then plotted onto a horizontal graph with pre-determined action and control lines, both above and below the centre of the graph. Over time the operator keeps an eye on the results and takes preventative action to ensure that, while the process may move up and down from day to day, it doesn't move too far from the centre of the graph. Once the process crosses the line into the action limits then action can be taken to bring the process back into line before the problem becomes visible. Such action can be taken without the need to halt the process. If the out of specification graph is not acted on quickly enough, then the problem is likely to get worse and become visible in actual photographs. Once this stage is reached the graph would have moved beyond both the action and control limits. The process is then deemed to be out of control and the lab should stop putting work through until the process is brought back into specification.

Glenn Guy