The root of the photo frame problem

1. Humidity problem: it is humid in the south, and it will deform with the change of air humidity even if it is not touched. You can refer to the technical details in Chinese painting mounting.

2. If the humidity around the book is different from that in the middle of the book, the book will bend upward, and the humidity is generally 12%. When you take it indoors, the humidity in the air is different from that of the book, and the water will be absorbed or evaporated from around or outside the book, so there will be a double stress problem and the book will bend down. This is the reason why the inner lining of the photo frame is deformed.