Hi Mark,

Just use soduim bicarbonate (bicarbonate of soda) from the cake ingredients aisle at Tesco's; dissolve it in hot water and then dunk the print. Make a test print to give you an idea of what happens at different strengths. I also find the washing soda from Tesco's works fine too, despite having a few other ingredients. Prints on different papers will also respond differently too, so it is worthwhile trying a few different paper brands.

Best regards,