creosote

[Ahmed]

Looking at the last photo, it looks like a very common brown stain. However, there is no evidence that a petroleum product was used as an impregnation for protective purposes. The color of "Carbonyl" is darker and its characteristic smell; however, there are colorless fungicides/insecticides...

[Obamot]

If you opt for an oil coating
I suggest you take a bottle of edible oil (e.g. rancid, which sometimes lays around in a kitchen or used for lubrication in a workshop or whatever) failing that, any oil that is not very sticky, of groundnut or first prize palm, to put some in a cup to test the application
in areas of 20cm X 20cm in three areas:
— one on the brightest part.
— the other on a non-shiny but treated part.
— and the last on an untreated part.

Then you measure the speed of absorption for each zone... repeat as many layers as necessary (the part not covered to date, will be of great use to you for comparison and evaluation of the number of layers required)
And you'll make your own deductions on how much you'll need to cover everything.

It is very possible that there is very good one (and still it is necessary to have the experience of the application) but I do not have enough experience with the stain (other than the one I have given above) with this type of coating, we are very tempted to take the first price which ends up flaking... While we are reassured by a quality guarantee logo (NF CE or other) Experience made with my teacher. of biochemistry.