Unissued specimen £1 note of National Bank of Scotland, 1893

Nevertheless, it was aware that advances in photography were expanding the counterfeiter's capabilities, so in 1885 the board ordered a full investigation into what could be done to create a new generation of copy-proof notes.

In negotiation with several note-engraving firms, the bank started testing which ink colours, features and designs offered the best protection. Each firm's trials were given to competitors to test whether they could copy them successfully; in this way, the bank learnt which measures were truly effective. The process took four years, but by 1889 the bank was ready to start work on its own new designs.

Aware that a portrait is a particularly good anti-counterfeit device, it decided to feature a vignette of the Marquess of Lothian, the bank's governor. When he saw the designs, he wrote to the bank's board, 'perhaps for the first time in my life, I shall feel that the more portraits of myself I have in my possession, the more I shall be pleased.' 

Colours were chosen to provide protection against counterfeiting, but - the bank's note committee declared - 'it is also desirable to have such colours as will please the eye, and have a clean appearance after the note has been in circulation for a considerable time.' Combinations of blue and yellow were found to be valuable, because it was difficult to reproduce both successfully by a single method. The new notes were finally issued in 1893, eight years after the project to develop them had begun.

National Bank of Scotland continued issuing banknotes until 1959, when it merged with Commercial Bank of Scotland to become National Commercial Bank of Scotland. A decade later, that bank became part of the Royal Bank of Scotland.