To make clean straight folds in cardboard, first make a crease along the line with a bluntedge such as a spoon handle, then fold against a firm straight edge.
为了使清洁直纸板折叠，先如勺子处理沿钝边行折痕，然后对折直边坚定。
2
The edge is as blunt as an old butter knife.
刃钝得跟一把老黄油刀一样。
《柯林斯英汉双解大词典》
3
No doubt it is the fate of all cutting-edge technology to eventually turn blunt, dull and outmoded, but that is a concern for another day, another era.