This is information re produced from my web site.
Up to date seven printing companies have been employed by the Royal Mail, some we have mentioned already elsewhere on the site.
The printers are:
Harrison & Son of High Wycome / Photogravure & Gravure
Bradbury and Wilkinson & Co. / Recess
John Waddington Security Printers / Lithography
The House of Questa, South London / Lithography & Gravure
Walsall Security Print / Lithography & Gravure
Joh Enschede en Zonen of Holland / Photogravure & Gravure (Recess High Values only)
De La Rue / Gravure & ( Recess High Values only)
Sorting Photogravure stamp from litho is not to difficult as all photo stamps are printed by a series of tiny dots. Under magnification they are easily seen especially in and around the margins, the Queens portrait and the value tablet. The pattern of dots show up as uneven edges.
Litho stamps on the other hand have crisp clear lines to these features.
Recent gravure issues were originally chemically etched and the stamps showed a clearer image. These were then modified to the most recent method EME or computer etched these computer etched stamps show a clearer sharper picture.
EME is short for Electro Mechanically Etched.
Four directions of print have been used with gravure printings, These are :
Sideways left or sideways right, upright and inverted.
To determine the direction of print on photogravure stamps again a good lens is required, the tiny dots (or points) show up as pointing in the print direction. Check it out, something for the beginner to do on a cold winter night perhaps!