This WWII German Mauser was not originally produced with the white lettering showing the date, manufacturers mark, and the other white lettering that you see in this photograph. I added this after the rifle was fully cleaned to help better show this item. I do the same thing with different parts of a radio, namely the knobs.
I have tried just about all of the tricks on the market to bring out this white lettering, crayons, white-out, chalk, finger nail polish, magic marker and so on. What I have found that works the best is a product called LACQUER-STIK.
All that is needed to accomplish this lettering is to simply rub the Lacquer-stik into the indentations and then carefully wipe off any excess. It is amazingly easy to use. Not only that, if you decide later that you have changed your mind, it can be easily removed with out causing harm. If you can scribble on a piece of paper then you have what it takes to use this product. On both sides of the center photograph is a picture of what a lacquer-stik looks like. It is similar to a piece of chalk or crayon.
The LACQUER-STIK's come in a variety of colors and last for years. Plus they are cheap!! I have been using the same piece of a LACQUER-STIK for years and at a price of under $3 each it is a bargain that should be in any restorers box of tricks. I purchased mine from Brownell's but I am sure they are sold else where as well.