Sandpaper can't clean the red paint on the plaster model. How to clean the plaster?

1. Scrape the polluted place by 2-3mm with a knife, and then fill the missing place with plaster. When gypsum is not completely solidified, it should be polished. After it is completely cured, it is polished with different sandpaper until the surface is smooth and flat.

2. Lightly polish the whole plaster model to make the overall appearance of the model almost the same;

3. The newly filled place shall be painted with white paint, dried and polished to be close to the surrounding conditions;

4. The whole plaster model is brushed again, which is totally unsatisfactory.