Would Like Help With Understanding Variations Of Shade In Photogravure Printing

In a recent discussion in another part of the forum (http://goscf.com/t/85211) I asked about the differences of shading on Italy Scott #221. I would appreciate it if someone could explain how these differences occur when printing a lighter shade of the same color as the rest of the stamp, even to the extent that the lighter shading appears to be missing.

Thanks in advance for any responses.

This is a photogravure stamp that was in use for a very long time. Photogravure cylinders get replaced. Variation occurs when the new cylinders are etched. Variation in the intensity of the light used to create the cylinders will result in variation in the depth of the etching of the cylinder.

NSK - thanks, very clearly presented and makes sense. I had been thinking more of some anomaly in the inking and printing; production of the plates as the cause is simpler.

Depending on the technology of the time when reprints were produced and the skill of the printer in matching colors, there can be quite a bit of difference in shades when individual stamps get reprinted. This is one of the cornerstones defining why collectors really enjoy collecting, for example, King George the Sixth era definitives.

The term shade might cause confusion and lead some to think of a variation of color as opposed to a difference in the strength of impression (amount of ink deposited in various areas of a stamp).

@shermae,

I agree that ink mixing caused many of the colour variations in British Commonwealth stamps. British Kinh Edward VII and George V stamps know many such variations as well. The stamps OP refers to, however, show a wide variety in the strength of the printing of coloured areas. That is unlikely to be the result of differencesin the ink mix. That would result in different colours of the coloured areas, not in different strengths of the coloured areas.

Also, in the thread to which OP refers, it was remarked that the more 'white' areas occurred mostly with early printings and the 'coloured' areas with the later printings.

shermae & rogdcam - my original post, found in the link cited above, had to do with a lack of a lighter shade of the one color of purple used, found in certain areas of the stamp where it was used as shading in those areas; not color variations between different stamps (multiple meanings of "shade" here). That's why I'm thinking that NSK's explanation fits better.

NSK posted while I was writing my reply, didn't mean to be redundant.

There are quite a few shades listed in Stanley Gibbons for Harrison photogravure stamps from places like Seychelles and Virgin Islands. Is it possible these variations are explained by how the plates were prepared?

I cannot say. 'Shades' as in variations in colours can have different causes. Deeper colours can be exactly that: deeper etching of the cylinder. It, however, can be due to a different ink mix. If you look at the Connoisseur Catalogue (available online), you will find 'shades' for stamps that have been printed from a single cylinder. But many Machin stamps have listed 'shades'. Even the fluors of the phosphor bars show wide variations that cannot be attributed to cylinders.