Is a substance that contains lard (pig fat) as one of its components regarded as impure (najis)?
Question

I work in a company that manufactures metal tables, and we use a substance that resembles ghee to polish and shine the metal. This “ghee” contains a substance that is extracted from lard, and when we use it, some of it comes off onto our clothes. My question is: is this substance impure, and are we not permitted to pray with this “ghee” on our clothes?
Praise be to Allah.Lard (pig fat) is impure according to scholarly consensus, so if it gets onto the Muslim’s clothes, he must purify them before he starts to pray.
Ibn Hazm (may Allah have mercy on him) said:
The scholars are unanimously agreed that the meat, fat, marrow, brains and cartilage of dead meat (animals that died without being slaughtered in the prescribed manner), and the meat, fat, marrow, brains and sinews of pigs, are all haram, and all of that is impure (najis)."(Maratib al-Ijma‘  p. 23).
It is only prohibited to eat pig fat (lard); as for using it for purposes other than food, such as using it to polish metal, wood and the like, that is permissible.
So if there is a compound which contains some lard, is that compound impure? We should look at the lard that is used: if it is a small amount and is absorbed into the compound, so that it leaves no trace of its colour, smell or taste, then the compound is not impure, because the impurity has no impact on it.
The same also applies if there is some manufacturing process through which the lard turns into some other substance, which is what the jurists call istihalah (transformation); the substance is deemed to be pure in that case.
But if the lard is still there, with its characteristics, even if it is a small amount but its traces can be detected in the compound, then in this case the compound is impure, and if anything of this impure compound gets onto a Muslim’s clothes, he must purify it before starting to pray, or he should have other clothes in which he can pray.
Ibn ‘Abd al-Barr (may Allah have mercy on him) said:
The scholars are unanimously agreed that one of the conditions of prayer is that one’s garments, the water and one’s body must be pure (tahir)."(At-Tamhid  22/242).
And Allah knows best.