What are the conditions that raw milk, just milked from a cow, should stand to obainin thick traditional Romanian smântână?
I can't give you the Romanian recipe but I doubt it differs much from Polish.
First, Start with cow milk. It must be genuine unprocessed milk - absolutely not cooked, UHT, preserved, skim, lactose-free or other 'inventions' where the natural bacterial flora has been killed and the milk will rot instead of souring.
Make the standard fresh cream. There were traditional tools for that but a centrifugal separator will do just fine, with far less effort; the technology doesn't 'spoil' this part.
Don't go over the top with fat content. The American creams are ludicrously fatty. 14-18% of fat content is normal, up to 30% is okay but really unnecessary and will make it harder to achieve the right results.
Then put the sweet cream in a clean ceramic jar, cover with a clean cloth that allows air through but will stop insects, and leave in a slightly cool place - temperature of order of 18 Celsius degrees (although 'cooler side' of room temperature is fine). Let it sit overnight and if you started with genuine unprocessed cow milk, it will sour and thicken into the traditional sour cream with a layer of transparent whey on the bottom.