A glass jar is a common household item that can be used to store everything from leftovers to office supplies. Aside from being versatile, glass jars are also quite plain. To gussy up that glass jar, you need is a special pen designed to write on glass and other non-porous surfaces.
Visit craft and art supply stores to see if they have permanent paint markers or pens specially designed to write on non-porous surfaces.
Purchase the pens in colours you wish to use. Be sure to read the instructions listed on the label.
Uncap the pen and use it to write on the glass jar. After writing, put the cap back on the pen and wait two minutes (or the length of time specified in the pen's instructions) for the ink to dry. After a couple of minutes, the ink should be completely dry and should not smudge when you touch it.
Remember that these speciality pens and markers are permanent, so you should carefully plan what and where you are going to write before you start. Expect to spend about £1.90 per pen, possibly more depending on the store.
Using markers and pens that are not designed to be used on glass will result in ink rubbing off the jar and onto your hands and clothing. This could permanently stain an article of clothing.