Decrease in Tone Value

What is it?
The reduction of the halftone dot in the print when compared to the original (film orprinting plate) is referred to as a decrease in tone value. In essence - abrasion of the printing plate.

How does it happen?
This phenomenon may already arise in prepress. In addition, various factors can also have a bearing on abrasion of the printing plate:

• Normal plate wear and tear
• Powder deposits on the blanket
• Unsuitable plate cleanser (a mixture of abrasive material)
• A pH-value in the dampening solution that is too low may slightly etch the edges of the halftone dots
• An alcohol content that is too high corrodes the plate film
• Rapidly volatizing cleansing solutions may damage the printing plate

Remedy:

• Use appropriate printing plates
• Use a suitable plate cleanser and certified cleaning solution when maintaining the printing plate
• Avoid using abrasive spray powder (calcium carbonate) use a based starch powder such as Superdot
• Always prepare dampening solution according to instructions (pH-value, alcohol concentration); the ideal dampening solution has a water hardness of 8 to 12°dH, a pH-value of 4.8 to 5.5, and a temperature ranging from 10°C to 15°C (50°F to 59°F)