With an oily needle pen (cherry blossom), every time you draw a picture, if you just finished drawing the line draft, apply an oily marker. Because they are all oily, it is easy to spend. Unless the color is changed overnight. In my experience, you can color on the reverse side of sulphuric acid paper, or spend some money to go to a large print shop. That kind of shop will have a machine that can do many things, such as copying and printing pictures. You can give him your line draft, tell him you want to copy, he will cram your picture into the machine, and it will be OK in 20 seconds. Any size picture of that machine can be printed, and it can be copied on sulfuric acid paper, and the price is very cheap. 15 yuan for A4. 12 yuan for A1.
You can use a marker that does not blur the photocopy line, which is the oil-based marker of the alcohol series. Secondly, try to avoid repeated sketching of lines when drawing to avoid paper damage. After the painting, there must be a certain drying time, do not touch it with your hands.
Generally large professional landscape companies do this to prevent the line draft from being spent by the marker. Some people like to paint on the reverse side of sulfuric acid paper. There are several kinds of sulfuric acid paper on the market, and one of them looks the same as high-quality.