La bouteille à l’encre.

>>>>>It means ' unfixed the problem or unclear stuffs '.In 18th century the people used 'clair comme la bouteille à l’encre'. It means 'It is like the ink'. Because the ink is with the color you can't see it. Now the people use it when they think the problem need to fix. Par exemple, 'Ce élection est la bouteille à l'encre'. 

La bouteille = The bottle

à = in

l’encre = the ink