Lighting Packaging | Half-tone Testing on a Heidelberg Press

With future lighting packaging and branding in mind, we have begun half-tone testing.

Half-tone is a printing technique which uses dots to replicate shades of grey or colour. Artwork or photographs typically have a continuous range of colours or greys. It’s not practical to print each colour or grey using separate inks, so half-tone is used to create the impression of a range of shades. Dots of different sizes and spacing are used to create the impression of continuous colour tones.

half-tone printing test sheet an example of half-tone printing an image printed using half-tone

Using the half-tone technique with letterpress printing and on the uncoated paper we use for packaging lighting is generally regarded as somewhere between difficult and impossible to achieve. Here at the Old Trouser Factory we looked on it as less of an impossibility and more of a challenge.

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The standard measurement of printing resolution for half-tone is lines per inch or LPI. The higher the LPI, the better the resolution. Good LPI figures are difficult to achieve using letterpress and the thick cotton based paper we use for our greetings cards because it is to hard to get the dots perfectly printed and positioned on the uneven and textured surface.

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After running the press for a while using a special half-tone test plate and making continuous adjustments, we are confident that 75 LPI is possible on our traditional textured cotton paper. On a more glossy and even surfaced paper, we think we can achieve 120 LPI. These are rather good figures for an original Heidelberg press which is into its second half-century. We are confident we can produce half-tones while continuing to use inimitable letterpress printing and recycled and kraft paper.

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