Offset Litho-printed transfer sheets printed at Sodecor in Italy use thick, matte-surfaced plastic (as opposed to the English thin, gloss-surfaced sheets). This doesn't affect the appearance of the applied transfer. There's a brief discussion of the difference on the Wall's/Look-In Star Wars page.
Because Rotary Gravure printing is very expensive to set up, it is rare to see transfer sheets using this method reprinted with minor changes. But Offset Litho printing is relatively cheap & easy, so from now on it becomes common to find transfer sheets with small alterations, or with varied (& sometimes multiple) serial numbers.
Letraset bought Linea Sodecor specifically to produce Kalkitos under contract from Gillette (the razor-blade company), although of course other series were printed at the Italian factory as well.
Two sheets provided by Letraset to encourage their clients to choose between BKT & Sodecor!
For a couple of years before the Italian purchase in 1976, Letraset did actually litho print some transfers. They didn't have their own press, but used BKT in Tonbridge, under the supervision of John Kingsland. For our purposes, almost all of these transfers would have been in the Decor-Craft range; when Sodecor was purchased, this arrangement naturally came to an end.
Typical Decor-Craft packs.
Kalkitos Serials are 6 digits starting with "05"; for the Sheet Serials that's all there is, but the Background Serials are followed by a batch number. Note that although Sheet & Background Serials follow the same sequence, they neither correlate nor overlap. It's unusual for Letraset products to print serial numbers on the backgrounds, & when it happens the corresponding number on the sheet is normally identical; not so with Kalkitos.
Being aimed at an International market, Kalkitos titles were usually printed in several languages. There were two basic sizes: Maxi (670mm x 240mm unfolded) & Standard (455mm x 125mm). They were produced between 1976 & 1981, but weren't promoted in the UK until late 1978. In fact, the set on the left (below) was a Free Gift given away in the 30th September issue of Look-In magazine to introduce the series.
The sample pack was a one-off extra small size; the set on the right is in the "standard" (small) size.
Other Litho-printed Letraset products use "L" or "LP" (P for Promotional) serial numbers, & when Thomas Salter went independent they used serial numbers starting with "TSL 090/" — although the "TSL" (for Thomas Salter Ltd) part was dropped quite quickly.
I don't really feel the need to say much else about Litho-printed transfers, since this is a mature technology which is still current. You can easily discover any technical details regarding the process for yourself online!
I am obliged to state that this document, the information contained within it, & its arrangement are all © Tom Vinelott 2007-2017.
Picture Credit: The SPLAT Scan Archives
© Tom Vinelott 2017