Purification and de-oiling

Oil contains many foreign bodies, the presence of which can have a detrimental effect on its drying process.
Such bodies include:

• water,
• plant mucus belonging to protein bodies
• and mineral salts.

Water and protein bodies can be present in a seemingly clean and clear oil. Only after storing it for a long time do they settle to the bottom of the vessel.
There are several ways to purify oil:
1. oil in covered vessels is placed in the sun for a period of two years.
Protein bodies and other impurities settle to the bottom and at the same time the oil is bleached in the sun.
In order to bleach the oil and at the same time thicken it, it is exposed to the sun in the summer in flat, wide vessels for 2 ÷ 3 days.
2 The oil is washed with hot and cold water, changing it frequently.
Washing is carried out in bottles by shaking them.
The water removes proteinaceous bodies from the oil.
To better separate the water from the oil, table salt is added.
Snow can also be used instead of water.
To remove water, the oil can be subjected to a very low temperature. The water freezes and is removed by filtering the oil at 0°C.
3. table salt also cleans the oil well (especially from water, as it is hygroscopic and pulls it from the oil).
It is good to make a mixture consisting of 1 part salt and 10 parts roasted gypsum instead of salt alone.
This mixture is rubbed with the oil and introduced into the oil.
The oil with this mixture is set aside for a few days and then the clean oil is poured off the top.
The mixture with impurities remains on the bottom.
4.The oil can also be purified by straining it through bone charcoal.
5) You can also purify and de-oil with Florida soil (filtering).
6.A fairly simple way to de-bleach and purify oil is to heat it to 150 ÷ 300°C. In doing so, the water evaporates, the proteinaceous bodies shear and settle to the bottom of the vessel, and the coloring bodies die.
Such oil has the ability to dry better and faster.
However, care must be taken not to overheat the oil. Heating should be stopped as soon as bubbles stop appearing on its surface and it begins to evaporate strongly.
7 You can also de-oil with a mercury lamp (ultraviolet rays).
Contaminated oil is not full-bodied, which reflects on the durability of the paint film.
In general, cleaning the oil from impurities is more important than de-bleaching, which occurs spontaneously directly on the painting. This is because the coloring bodies present in the oil are not permanent and quickly decompose in the light.