What are the protective measures for a painting on plain white paper? Is there any paper that won't turn yellow easily if it is kept for a long time?

This can only be done with a glass bezel. Stick a back plate on the back glass, try not to have gaps, and seal the back with tape, but it will turn yellow after a long time. As for the protection measures of paper yellowing, it must be dry, and it is best to isolate the air and avoid light.

If you don't want to show your paintings, you can put them in a dry, dark and relatively isolated environment. Dense cabinets or something. Generally, paper will change after a long time, so there is such a thing as a dense cabinet.

What paper won't turn yellow? It's not nonsense to buy paper that is a little yellow and turns yellow slowly! Because white paper is bleached by wood pulp, it is easy to oxidize. Besides, yellow paper can't be seen at all.