As a result of investigations and having con-suited the practical officers of the Post Office and Stamp Office, my Lords are of “ opinion that the most secure arrangement will be to use good black printing ink, “ prepared in a peculiar manner, for the purpose of obliterating the stamps, and in “ order that the black obliteration may readily be distinguished, to substitute some “ other colour for the black ink now used in printing the Penny Stamps.

Subsequently, however, Messrs. Perkins & Co., the contractors, have, after “ a great variety of experiments, succeeded in procuring a red ink, which not only “ affords a good impression, but possesses the additional advantage of being readily “ acted upon by nearly all the chemical agents which are likely to be resorted to for “ removing the obliterating mark................
“ My Lords are, therefore pleased to direct that in future to “ print the Penny Postage Stamps with the new Red ink ....

The blue tinge that created the Ivory Head effect, originated in the red ink (because no discolouration took place while the black ink was in use), the degree of blueing which manifested itself was governed entirely by the dampness of the paper at the moment of printing. It was necessary that the paper employed for printing from the line-engraved plates should be damped, and it would appear that when this was insufficiently done, as no doubt frequently happened by inadvertence, the very slight amount of moisture present was insufficient to set up the chemical action from which the blueing originated, and consequently such impressions are found to present no trace of it.

That the discolouration took place at once, and was not the effect of time

It was discovered that the red MX cancellations were being removed from the penny black in order that they could be reused. This prompted Rowland Hill initiate the Rainbow trials, whereby different inks and printing techniques were tested in order to overcome this problem. The goal was create an ink which would be more permanent than the ink used to print the stamp. It resulted in only the black MX cancel being used, and red-brown printing ink, the combination of which clearly showed the cancel.