The early model diesel engines used a simple formula of 33% ether, 33% kerosene or naphtha and 33% oil. The 1% could be amyl nitrite or something like that at the time.
Half way down here in this page they go into a good discussion of the different model diesel engine formulas that people use.
http://www.colinusher.info/Model%20Aircraft/fuel.html
Nowadays we can't get ether easily anymore, and the extra additives are hard to get too. So one can look and see if any of the brands of engine starter fluid has ether in it or not. some brands have more ether in them that others do. Then one can use some Cetane Booster fluid as a substitute for the additives we used to get. But then with you being in Croatia, you might have access to ether where we don't here.
Castor oil can be the medicinal castor oil they sell at the phamacy, but you need to get the castor oil without sugar or any flavor additives added to it. Here many of us use the Klotz Benol brand as it has a additive in it to allow it to mix better in the fuel. Our other brands are usually SIG Castor oil, etc. In the past they used heavy weight automobile oil such as 50 to 70 weight oil. The 50 weight aircooled motorcyle engine oil works well too. Oils at the time had very low sulpur content or zinc additives, so you could look for oils like that too.
With the old bushing engines with lapped pistons you want to have 25% oil in the fuel or more even depending on the engine type.