<H1>What is Ink Density in Offset Printing?</H1>

Ink density in offset printing is the measurement light that is reflected from an ink. It is essentially the measurement of how dark and ink is. Every ink or substrate has the ability to stop or absorb light. The less light that is reflected back, the higher the density is considered to be.

How is ink density measured?

It can be said the more ink that is supplied to a surface, the less light it will reflect. However the formula below negates this theory.  The reason is that at a certain point, adding more ink will not make the image darker.

It is measured by means of this formula:

Density= log101/Transmittance = log101/Reflectance

Here is a graph that illustrates this point.  At the upper end of the graph we see the darkness levels off.  Printers try to find the right thickness of ink so that conditions on the press are stable and proper color is achieved. Offset printers use what is called a densitometer.

What is a densitometer? 

A densitometer measures how much light is reflected back from a given surface. In offset printing, some printing presses will have this device mounted right on the press, measuring in real time. Another densitometer is offline, usually near the printing press where the pressman can use it to take manual measurements.  Here is a picture of one. 

The densitometer uses the formula above for calculating a value.

Offset printers will use a printed sheet like the one above for testing, but the more common method of testing is from a color bar as shown above.

Note the long line of colors at the top of the printed sheet.  Offset printers put them to measure the density of offset printing inks.

What are optimum Ink Density Measurements in offset printing?

Though ink manufacturers may suggest slight variations, below is generally considered the industry standard for CMYK offset color printing.

C 1.45 +/- 0.10

M 1.45 +/- 0.10

Y 1.0 +/- 0.07

K 1.7 + 0.2 - 0.05

Since densitometers cannot see light, only how much light is reflected, the readings are a one-dimensional variable that pressmen can use to quickly evaluate how much ink is being printed. This convenience allows them to bring the offset printing press to its optimum quality parameters.

Ink Density and Gray Levels

Since densitometers cannot see color, they simply measure how much light is reflected. Therefor these results are sometimes simply referred to as gray levels.  

Conclusion

Ink density in offset printing is simply the measurement of the absence of light. Offset printers use tools to measure this difference to determine how dark an ink is. 

Once offset printers know the density, they can make adjustments on the printing press that will allow them to have stable and high quality parameters throughout the print run.