Ultimately, it occurred to Rowland Hill that “as the means which were successful in removing the printing ink obliterant were different from those which discharged Perkins' ink, a secure ink might perhaps be obtained by simply mixing the two.”[172] The device succeeded, the ink thus formed proving indestructible; and all seemed likely to go well, when a fresh and very disagreeable difficulty made its unwelcome appearance. To enable this ink to dry with sufficient rapidity, a little volatile oil had been introduced, and its odour was speedily pronounced by the postal officials to be intolerable. Happily, means were found for removing the offence; and at length, a little before the close of the year, all requirements seemed to be met.[173] It had been a time of almost incessant anxiety. For more than six months there had been the earlier trouble of securing a suitable design for the stamps, and then, when selected, the long delay in effecting their issue; and now, during another six months, this later trouble had perplexed the officials and their many sympathisers. In the end, the colour of the black penny was changed to red, the twopenny stamp remaining blue. Thenceforth, oleaginous inks were used both for printing and for obliterating; the ink for the latter purpose being made so much more tenacious than that used to print the stamp that any attempt to remove the one from the other, even if the destruction of both did not follow, must at least secure the disappearance of the Queers head. A simple enough remedy for the evil, and, like many another simple remedy, efficacious; yet some of the cleverest men in the United Kingdom took half a year to find it out.