Natural Wood Stain
About DIY Stain
Iron oxide stain produces different colors depending on the type of wood and how long the mixture was allowed to oxidize. It turns a grey on cedar, but makes pine brown. On the example above - either it's the tea that makes it grey or this wood is not actually pine.
- Steel wool - 
- White Distilled Vinegar
- Many cement/concrete integral colors are Iron oxide based and can be purchased in concentrated liquid suspension or dry powders and are available in a few colors at most hardware stores or can be custom ordered. There are many other more rare colors of minerals used for painting frescos or plastering with lime mixes, but the cost goes up with rarity and often color intensity.
- Wood charring is also an old preservation and coloring technique, but often involves a lot of fuels for carefully burning off a flammable mixture made with boiled linseed (flax) oil. Shou Sugi Ban is a Japanese method of charring. It may also be labor-intensive to brush off excess charcoal depending on the desired effect. Such techniques may also not be advisable for items like furniture that people in white suits might sit on.