It sometimes happens that you don't use fountain pens for a long time or you replace cartridges before they are emptied and think you can use the remaining ink again later (at least you think so, but you rarely do it, and if you do, you should do it quickly, as the test shows). My curiosity was piqued again and I thought it could be fun to measure how quickly ink in fountain pens (or cartridges and converters lying around) dries out.