Here are a couple of recipes I came across a while back. I can't remember where I got them from, so apologies to the original authors. If you use carbon steel for your blades, as I do, you know that it will develop a patina over time and that the patina is helps protect the blade from rust. The people who buy your knives don't always see it that way and wonder about the "stain" that is growing on the blade. This is especially prevalent when people use our knives to cut food. Here's a little mixture you can use to develop a protective patina on the blade before you pass it on. Make sure the blade is clean and grease free before you start. Create a 50 - 50 mix of tea and fruit juice (preferably something like orange or grape with high acid content.) Warm the mixture in the microwave and stand the blade in it for 10 minutes, moving the blade from side to side every couple of minutes. Rinse the blade in water and check the results. You can repeat the process to deepen the patina. If you prefer to get more creative, you can develop a patterned patina. You can use this to give a blade that "aged" or "forged" look or just to add a design. Again, always clean and degrease the blade before you start. Create a mixture of malt vinegar and garlic paste so that it is thick enough to stay on the blade. Apply the mixture all over the blade with a small brush or your finger (If you don't mind explaining where that smell comes from. :blushing Let it sit for about 40 minutes. Rinse the blade thoroughly. Create another mixture from equal parts tomato ketchup and HP sauce. Using a brush, sponge, stick, etc. apply the mixture to the blade in swirls or stripes or sploches to create a pattern. Let it stand for about 30 minutes Rinse the blade and inspect. You can repeat the second mixture if you want to add to the pattern. You can also play with the times to make the base or pattern lighter or darker. Don't worry about ruining the blade. If you don't like the result, a rub down with some fine sandpaper will remove all traces of your experiment.