Burned letters in wood and cardboard

For a long time I was searching for a solution to permanently engrave letters at home. I finally had the time to test this idea to burn letters with the electric soldering iron.

However my current tool has 30w power. This seems to be insufficient for covering large surfaces and working fast.

 I will post some updates here after testing a better tool. I am working on a sketch book with wood covers, hoping to be able to engrave letters with a good precision, even on slightly textured surfaces like plywood.