Wood that's exposed to the sun's UV rays over an extended period of time will darken and even turn gray. This weathering happens because the sun causes chemical changes to the tannins in the wood, kind of like oxidation.
Black spots are formed when the wood is exposed to metal and moisture. Like a wet glass or leaky vase. This causes a chemical reaction from the tannic acid and water. The chemical reaction leaves black spots on your wood.
Improper curing usually happens from over applying the stain. In very hot and humid climate types, mold and mildew can actually begin to form on the surface of a deck stain causing it to appear darker. In extreme cases, mold and mildew can grow below or in the stain, further darkening the appearance.
The wood is usually far too damp and poorly seasoned, which is the main cause of wood turning black and not burning correctly. But other factors might also play a role in why woods turning black and doesn't burn.
Liquid Detergent and Cold Water Remove Black Stains
It involves the use of liquid detergent and cold water to facilitate the removal of black marks. Note that the combination of liquid detergent and cold water is best used for removing urine and ink spills on hardwood floors.
This is known as zebra stain. Zebra stains happen when iron or manganese darkens the browning and makes it turn black. Sun Exposure. If your wood product is left outside and exposed to the sun, over time it will darken (like a sun tan) and may make the wood appear dirty or damaged.
When you have black spots on a hardwood floor that clearly are not growing and spreading, if you can't simply wipe the floor clean, it's not mold. You have other issues, and they are likely not very serious.
The biggest reason for a deck stain turning black is mildew. All wood surfaces need to be cleaned correctly prior to staining.
The discoloration is caused by moisture, and it can sometimes be removed the same way white spots are removed. Buff the surface lightly and evenly with No. 0000 steel wool dipped in linseed oil. Work with the grain of the wood, rubbing evenly on the entire surface, until the white haze disappears.
The question of the temperature of the carbonization is important; according to J. Percy, wood becomes brown at 220 °C (430 °F), a deep brown-black after some time at 280 °C (540 °F), and an easily powdered mass at 310 °C (590 °F).
The water soaks into the wood and as it evaporates out of the wood it brings along the colored extractives which can then become visible on the surface. In some cases water-soluble tannins may react with minute particles of steel on the surface forming dark, iron tannate stains.
Pre-staining the wood with black tea or coffee can produce more tannins and thus, darken the wood. An oxidation solution with apple cider vinegar can also produce a slightly darker result without the need for a pre-stain.
Before you use a stronger bleach on any piece of furniture, try laundry bleach; it usually does the trick. Oxalic Acid: Oxalic acid, sold in powder or crystal form, is used to remove black water marks from wood. It is also effective in restoring chemically darkened wood to its natural color.
Other dark growths that may look "black" on wood surfaces include black yeasts such as Aureobasidium, often A. pullulans, as well as some of the most common species of Cladosporium sp. and Alternaria sp., some of the more common dark molds that we find on plywood roof decking in attics and on occasion on rafters.
Wood rot presents as decay, and mold presents as discoloration, usually black or white. Wood rot is a dangerous but avoidable condition often found in the wood of older houses.
Combine equal parts vinegar and warm water in a spray bottle and spritz this solution on the mold. Let the solution dry for one hour, then wipe down the surface with a moistened cloth, followed by a dry towel.
Killing mold on wood furniture. Use diluted dishwashing detergent or diluted bleach and wipe down the furniture. Make sure the room is well ventilated to help the wood dry as quickly as possible. Repeat as necessary.
Wipe wood furniture with a barely damp microfiber cloth to remove dust and grime. (Use a cotton cloth to avoid damaging the wood.) Quickly wipe it dry with another microfiber cloth. Don't let water sit on wood since it can warp the surface.
As a result of oxidation, wood subjected to heat treatments tends to lighten with time. Changes in colour also depend on the finish any particular wood was treated with. These phenomena are associated with the very nature of wood and have always been part of its beauty.
Removing the black stain from Oak:
To get rid of the black stain from Oak (or other timbers) we use Oxcillic Acid.
WD-40 is a lubricant for things like squeaky doors and rusty hinges, so it's made with petroleum oil. Using this on wood can darken the surface—giving the appearance that it has lifted a light stain—but it can't actually remove water stains.
Watermarks -- or water stains -- are often caused by cold glasses, spills, or hot dishes places directly on the wood. Luckily, though, they aren't always permanent. This guide will guide you through the process of removing these stains. But first, remember: even a quick touch-up can damage an heirloom.
You can remove water stains from wood with household products like distilled white vinegar, toothpaste, and even mayonnaise. Light stains are newer and can be removed using surface treatments like polish. Dark stains are older and have mildew growth; you'll need to sand the piece to get rid of them.