This ink is not for fountain pens and it required an extreme heat (ie: stove or
hot halogen light) to make this invisible ink to be visible. I thought the ink
will be visible from the heat of my finger such as the one in some check book,
but it doesn't. I have to put the paper directly under my halogen table light
for 7-10 seconds to change this ink into a blue shade. Not worth the money.