To spice it up, Croatian food company Podravka uses thermoreactive ink to print part of their annual report - a recipe book appropriately titled Well Done - so you have to bake it in the oven first before it can be read!
“Well done” created by Bruketa & Zinic is the new annual report for Podravka, the biggest food company in South-East Europe. It consists of two parts:
• a big book containing numbers and a report of an independent auditor
• a small booklet that is inserted inside the big one that contains the very heart of Podravka as a brand: great Podravka’s recipes.
To be able to cook like Podravka you need to be a precise cook. That is why the small Podravka booklet is printed in invisible, thermo-reactive ink. To be able to reveal Podravka’s secrets you need to cover the small booklet in aluminium foil and bake it at 100 degrees Celsius for 25 minutes.
Link - Thanks Aaron Larney!