Oil painting mediums can deteriorate when exposed to air. They can also leak in transportation. If they are solvents they can evaporate.
So some special containers are sometimes used for oil painting mediums.
For those who encounter the lids of these containers for the first time, opening them may seem baffling.
These photos and instructions should help get you past the initial confusion so that you see that they are really quite simple to deal with. Once you know how, it’s easy.
Note: to prevent any dust entering the opening during the seal removal I recommend that you wash the top before you open your container.
Pull out nozzle style opening
Metal inner seal style opening
Click on the underlined link to go to the Oil Painting Mediums Department on the Jackson’s Art Supplies website.
Postage on orders shipped standard to mainland UK addresses is free for orders of £39.