What does wood bleaching mean? Methods and means of bleaching wood. wood

Wood bleach is a preparation that allows you to “whiten” a wooden surface, regardless of its purpose and type of use, and also protect it from fungal damage.

The need for whitening occurs when wooden product(log house, furniture, finishing elements) lose their natural color, they develop a yellow or gray tint, which is caused by external factors (atmospheric phenomena, exposure to high temperatures etc.).

The principle of operation of the bleach is based on the oxidation of wood, during which the discoloration of lignin occurs, which is a substance that holds together the cellulose fibers of wood and is located in the walls of plant cells and the intercellular space.

Composition of wood bleach

Currently produced by industry a large number of different brands of wood bleaches. They can be classified into two categories, these are:

• Contains chlorine.

This group of drugs includes bleaches made using potassium or sodium hypochlorite, chlorine dioxide or bleach.

• Without chlorine containing components.

This group contains drugs that contain hydrogen peroxide, as well as ammonia, alkali and oxalic acid.

The best wood bleaches

There is a wide range of bleaches on the market for wood processing products. different brands, domestic and foreign manufacturers.

Different brands of drugs differ in chemical composition and cost, packaging and options for use.

Neomid 500 is a chemical composition used for bleaching and disinfection of wood. Used for treating wooden surfaces indoors and outdoors.

When bleaching with Neomid 500, the wood returns its natural color, thereby increasing its grade, the structure of the wood does not change, and its properties are preserved.

In addition, this bleach destroys fungal formations that destroy the structure and color of wood.

Neomid 500 is used as an antiseptic for processing pellets (fuel granules), which increases their shelf life.

Advantages of the drug:

• environmental Safety;
• high quality of goods;
• optimal price-quality ratio;
• ease of use;
• versatility of use depending on the type of wood being processed.

The product is certified and sold in cans of different packaging - 1.0/5.0/24.0/35.0 kg.

Manufacturer: EXPERTECOLOGY-NEOHIM group of companies, Russia.

Senezh Effo

This bleach is used to lighten wooden surfaces that have lost their natural color when exposed to atmospheric conditions and fungal infections due to prolonged use and exposure to ultraviolet rays.

Senezh Effo is used to disinfect fungal infections of various stages on the surface of wooden products and finishing materials.

This preparation is used when processing planed and chopped lumber that has not previously been treated with paints and varnishes. Bleach can be used indoors and outdoors and should not be used to remove blue stains from inside wood grain.

Advantages of the drug:

• does not contain chlorine, based on an oxygen-transfer agent;
• provides deep whitening;
• does not lose its characteristics when long-term storage and freezing;
• does not form chemical burns on the treated surface;
• capable of removing all types of organic damage;
• safe for humans and animals when used as directed;
• has a pleasant lemon smell;
• is an explosion and fire safe substance.

Sold in various containers and packaging.

Manufacturer: Senezh-preparaty company, Russia.

Homeenpoisto

Homeenpoisto is a hypochloride solution designed to remove mold from wooden surfaces. This product is used to clean painted and unpainted surfaces.

This is a jelly-like solution that contains sodium hypochlorite and sodium hydroxide, which are aggressive substances that require special care when working with them.

Sold in canisters of 1.0 and 5.0 liters.

Manufacturer: Tikkurila, Finland.

Sagus

This product is an effective means for bleaching wood both indoors and outdoors. Sagus is used when processing chopped, sawn and planed wooden surfaces.

The solution removes darkening on the surface of wood of various origins (from external influences, under the influence of time), and also serves as a disinfectant that removes biological lesions (microorganisms, insect larvae).

The advantages of this drug are:

• possibility of bleaching inside the wood surface (deep penetration);
• high efficiency;
• retains its positive properties during long-term storage and freezing;
• does not cause chemical burns to the treated wood;
• capable of removing all possible types of damage to wooden surfaces;
• fire safe.

Sold in cans, packaged in 5.0 and 10.0 liters.

Manufacturer: Sagus group of companies, Russia.

Fongifluid Alpa

Fongifluid Alpa is an aqueous solution based on fungicidal (antifungal and anti-mold) substances. The drug is intended to destroy various types moss and lichen, as well as mold and microorganisms.

Used for outdoor and interior work as a preventive and therapeutic agent.

Sold in cans of 0.5/2.0/5.0/20.0 liters.

Manufacturer – ALPA COATINGS Company, Russia – representative of the SOMEFOR® concern, France.

Caution when working with wood bleaches

Working with wood bleaches requires care and caution; in addition, you must follow following rules that ensure the safety of work are:

1. The work must be carried out by trained personnel who are familiar with the hazards when working with specific type bleach.
2. Personnel must be provided with special clothing and personal protective equipment (gloves, goggles, and for some types of materials - a respirator).
3. Bleach should be stored and prepared only in special plastic containers.
4. When applying, use a serviceable tool (brushes, rollers, etc.) made from synthetic materials.
5. All work on further processing of wood is carried out only after the bleach has completely dried and the surface has been cleaned of its residues (rinsing).

Treating wood with bleach

Treatment of wooden surfaces with one or another type of bleach is carried out in accordance with the operating instructions that come with the specific type of preparation.

The instructions describe what needs to be done before application, how to apply the product and how long it will take for it to dry.

Besides this, there is general recommendations that can be used when treating wooden surfaces with bleaching agents are:

• When performing work, do not mix various brands bleach.
• After the preparation has dried, the surface should be washed with clean water.
• If any area of ​​the wooden surface is severely damaged, it is necessary to treat this area with a more concentrated solution of the drug.
• The work must be carried out under conditions corresponding to the mode of use recommended by the product manufacturer.
• When working with bleaches, you must read the instructions for use and follow safety precautions for working with substances of this kind. This applies to use individual funds protection, as well as providing ventilation, when performing work indoors.

Wood bleaches are effective drugs, allowing you to extend the life of wooden products and give them a beautiful and natural appearance.

How to bleach wood. How can you bleach wood? Choosing a wood bleach.

Wood bleaching is widely used when it is necessary to soften the natural tone of wood, remove unwanted stains, and give wood an attractive appearance. There are several methods of whitening.

Whitening wood with Neomid 500 impregnation.

What to do? Trouble! My frame has turned black wooden house. Everything was covered in blue—blue, stained with fungus, and there was terrible mold inside the log house! What to do? Help!

This is often the beginning of a conversation with an inexperienced builder of a log house or a wooden bathhouse.

They also ask: how to bleach and remove mold and wood-staining fungus? I heard that there is a means of impregnation for these purposes - wood bleach, but I don’t know where to buy it and what is the price of this wood bleach?
The question is answered by the honored builder of log houses, builder of country houses wooden houses and ban Yudin V.Yu.

In my experience, wood bleaching is required if it is infected with wood staining fungus and blue (white) mold. Wood bleach also helps in the fight against the most dangerous pest wood - house fungus and blue mold. In my practice of making log cabins and building wooden houses from timber, very often the wood suffers from this scourge. Moreover, it would be nice if the wood turned black, turned blue and became stained and retained its physical qualities. But this is not the case here. Wood from harmful fungus and mold very quickly begins to deteriorate and lose its physical properties. Chemical properties, in short, if you do not apply intensive bleaching of the wood, intensive rotting and destruction of the wood begins. All this can happen very quickly. Therefore, if you find signs of fungus - dark (or blue) spots on the wood, then you need to immediately buy the most effective wood bleach Neomid 500 and immediately use it for its intended purpose - bleaching wood (wood) logs wooden log house- a wooden house made of timber. Wood bleach Neomid 500, in addition to bleaching, will help you disinfect logs and timber from fungus and with a guarantee destroy fungal spores and mold spores.

Many people ask the question whether there are others, besides Neomid 500 wood bleach, with a stronger spectrum of action. I can say with confidence that there is nothing else like it effective remedy does not exist in Russia. Wood bleach Neomid 500 is the most effective and radical chlorine-based composition. Not one type of wood-decaying fungi (mushrooms) can resist its action. Neomid 500 bleach destroys all known types of wood pests.

Therefore, my summary is this - if you find suspicious black, yellow, green or blue spots on the surface of a log house (on logs, beams or lumber), you should know that your wood has begun to become infected with a wood-staining fungus (fungus). There is only one remedy against this - Neomid 500 wood bleach!

People often ask: how many times should a log house be processed? wooden house for the final destruction of fungus or mold. My opinion is that in this case it is best to bleach the wood two to three times with an interval of 24 hours.

Helpful tips: when bleaching wood after its wood has been damaged by a fungus, you should keep in mind that the effect of bleaching wood from blue and black colors (wood-staining fungi) will be much stronger if the wood is treated twice with an intermediate drying interval of 24 hours. The wood-staining fungi and their spores that survived the initial treatment - bleaching the wood - will be completely destroyed by repeated bleaching!

With your own hands

What other wood can be bleached?

During the construction period, wood not treated with antiseptics darkens from exposure external factors and mushroom colors (mold, blue).

Darkened wood can still be bleached, but not in all cases. Only superficial damage to wood is bleached. The depth of wood bleaching is determined by the penetration depth of the bleach, which rarely exceeds 3 mm. If the lesion is too deep, then attempts to bleach the wood may be futile, because... “blue” may be visible through the translucent bleached layer of wood.

Wood must be bleached if the wood texture will decorate the interior or exterior of any building.

But the wood does not need to be bleached at all if there is no requirement for the appearance of the wood. special requirements, or the wood is planned to be painted over with a covering coating or sheathed with another material.

It is important to understand that bleaching wood affected by mold and blue stains is a much more labor-intensive and very expensive process compared to antiseptic treatment.

To prevent wood from being damaged by mold and staining fungi, it is treated with a hard-to-wash antiseptic ZELEST STAGON. The antiseptic is manufactured in accordance with modern environmental requirements; it does not emit odor and does not change the color of the wood. The product is supplied in the form of a liquid concentrate. A working antiseptic solution is easy to prepare; for this, the concentrate is diluted with water in a ratio of 1:9.

Repair

Operating principle of wood bleaches

Wood bleaches work one at a time general principle: Essentially, wood bleaching is an oxidation process that leads to discoloration of lignin pigment colors, as well as destruction and discoloration of wood-staining fungal cells.

Conventionally, wood bleaching compositions can be divided into chlorine-containing bleaches and chlorine-free bleaches.

The first include bleaches containing sodium or potassium hypochlorite (NaClO or KClO), bleach Ca(OH)ClO, chlorine dioxide ClO2, etc.

The latter include bleaches based on hydrogen peroxide (H2O2 2H2O.), in combination with ammonia NH4NO3 or alkalis and salts (NaOH, Ca(OH)2), oxalic acid (H2C2O4), etc.

For all of the above substances, the process of bleaching wood comes down to bleaching colors of different nature active oxygen radicals.

In bleaches based on hydrogen peroxide, the bleaching process occurs due to the oxidation of colors by the peroxy group –О-О- and partially due to the oxygen that is formed during the decomposition of peroxide compounds: 2H2O=2H2O+O2

Characteristics

How to bleach wood?

If you want the paint to lie evenly on the wood and not change its color after drying, then you need to bleach the wood. And any stains on the surface of the wood can be masked by bleaching. So let's figure out how to bleach wood.

First you need to decide on the most suitable means for whitening. After all, you can bleach wood using hydrogen peroxide, titanium peroxide, bleach and oxalic acid. You might be interested in a vertical milling machine.

If you decide to bleach with oxalic acid, then first treat the surface of the wood with a solution of sodium hydrosulfite, and after a day, apply oxalic acid to the surface and after five minutes rinse it with water.

After bleaching, you can remove the resins with a bleach solution. To prepare it, you need to pour 30 g of soda ash into 100 g warm water, and then cool the water and add 15 g of bleach. Treat the wood with this solution and then rinse it off with water.

You can qualitatively discolor wood using a 30% solution of hydrogen peroxide. But be sure to blot the wood before applying peroxide. hot water, dry and treat with ammonia.

It is very good to bleach deciduous wood with lime milk. To prepare it, dilute 10 grams baking soda 350 grams of water, and then add 80 grams of bleach.

Well, you can quickly discolor the surface of wood with a solution of acetic or citric acid.

How can you bleach wood?

Bleaching wood, boards, logs, houses

What is the wood bleaching process? How to restore the natural, natural light color of the wood of the logs of a wooden house? What is the best wood bleach to use for bleaching boards, lumber, timber and logs?

Wood-staining fungi give wood a bluish-gray color called “blue” or “blackness,” but there are fungi that stain wood brown, yellow, green, or pink. You should know that blue stain damage is not only an optical defect, and at first glance does not seem to destroy the wood. However, we must not forget that it is the “blue” and “blackness” that creates a breeding ground for the growth of wood-destroying fungi, which directly affects the strength and durability wooden structure home or bathhouse.

If the original color of wood has changed as a result of improper storage, it can be bleached using a special wood bleaching composition. The quality of such bleaches on the market varies and depends on chemical composition. One of the real bleaches for wood - logs, boards and lumber, the quality of which has been time-tested for Russian market, is the composition of “Sagus”, “Meekout”, Neomid 500, Septol 50 and “League Bioshield”.

These bleaching compounds are designed to return wood that has wood stain and mold damage back to its original condition. decorative properties, to give wooden surfaces darkened over time the original color and texture of fresh wood.

To make a wooden product from pine, spruce, cedar. linden or poplar has become pure white without losing its texture, use a solution of a colorless one of these bleaches.

Processing and bleaching of wood, namely bleaching of lumber and boards, should be carried out in well-ventilated areas or outdoors at temperatures not below zero.

The consumption of preparations when bleaching wood depends on the nature of the lumber and is 150-300 grams per 1 square meter.

In some cases, when the depth of penetration of wood-staining fungi into the wood of a tree is more than 3 mm, it is necessary to treat the wood two or three times.

When bleaching wood - boards, beams, logs and lumber, it is extremely important to decide and purchase a high-quality wood bleach

Choosing a wood bleach.

SENEZH NEO - Product for soft bleaching of wood and removal of surface lesions

SENEZH NEO is intended for gentle surface lightening of wood darkened as a result of fungal stains, exposure to atmospheric and temporary factors, solar UV radiation, as well as the removal of surface biological damage of various natures.

SENEZH NEO is used on planed, sawn and chopped wooden surfaces, previously untreated paint and varnish materials, indoors and on outdoors. The product is not used to remove blue stains in wood. It is allowed to use the product on concrete, tiles, stone, tiles, bricks and other materials to remove mold, moss, algae and lichens.

Gently bleaches wood due to a mild oxidizing agent
Doesn't have unpleasant odor, does not emit toxic compounds
Particularly convenient for interior work, does not require special precautions
Visibly improves the appearance of damaged wood
Does not destroy the structure of wood, does not damage the surface
Effectively removes superficial biological lesions
Preserves the natural smell and breath of wood
Increases the grade of affected lumber
Does not affect the strength, adhesion and paintability of wood
Fire- and explosion-proof material

The working solution of SENEZH NEO is prepared immediately before use by mixing Components A and B in a ratio of 1:4; Apply generously to the affected areas using a brush, brush or sponge in several doses with an interval of 20-40 minutes. Use the prepared working solution within 2-3 hours. Process vertical surfaces from bottom to top. Before painting, rinse treated surfaces with water, rinse vertical surfaces from top to bottom. Large surfaces are usually bleached completely over the entire area.

The actual consumption of the working solution depends on the degree of damage to the wood and is usually 200 - 400 g/m2.

A two-pack, on-site formulation based on active oxygen.

The bleaching mechanism of SENEZH NEO is based on the reaction of free radical activation of an oxidizing agent with the release of active oxygen, which, without damaging the wood, oxidizes darkened lignin fragments and fungal stains, brightening and disinfecting the surface.

Work with protective glasses and gloves. Avoid contact with exposed parts of the body or ingestion. In case of contact with eyes and mouth, rinse with water. Hazard class IV (low hazard) according to GOST 12.1.007. Approved for use by Rospotrebnadzor of the Russian Federation. Fire and explosion safe. Dispose of as household waste. Do not mix with other formulations! Avoid contact with metals!

Storage and transportation

Store and transport SENEZH NEO in a hermetically sealed container from the manufacturer in a cool place, out of reach of children, away from food products. Keep away from direct sunlight! Avoid heating! Shelf life – 12 months. It is allowed to use after the expiration date with an increase in the consumption rate.

Component A and Component B of SENEZH NEO are packaged in polyethylene canisters with a net weight of 4 kg + 20 kg, respectively.

Russian Certificates
Certificates of Belarus
Certificates of Ukraine

http://imc.com.ru

In the warm season, from May to October, wood is easily affected by wood-staining fungi. They do not cause any particular damage to the tree, but the presentation is lost because the wood turns blue and black. In addition, blue color creates a breeding ground for wood-decaying fungi. The color of wood exposed to open space also changes under the influence of ultraviolet radiation, first acquiring a yellowish tint, gradually turning into a dirty gray. The problem of mushroom stains can arise in sawmilling, during the storage of sawlogs and lumber, during the construction process, as well as in a constructed wooden house.

It is especially offensive to the owner of a newly built house - a black log house is not at all pleasing to the eye. You can combat this sad fact in several ways: paint, sheathe it with other material (for example, siding), sand or trim off unsightly stains and, finally, use chemical bleaching, which will be discussed. Bleaching can be used both in primary woodworking and in wooden house construction, carpentry and furniture production, as well as in the pulp and paper industry. The natural color of the wood is restored, and the structure is completely preserved. However, it should be taken into account that lumber, which will subsequently be subjected to further processing, can only be bleached superficially; during planing and profiling, colors may again appear on its surface. Another thing is a wooden house. It will look like new. In furniture production, bleaching is used to make the wood surface more light color, evening out the color of the core and sapwood and removing stains. Pulp bleaching is a complex chemical process carried out using a variety of chemicals and technological equipment under conditions of high temperatures and pressure.

What types of wood bleaches are there?

Conventionally, bleaching chemicals can be divided into two groups: those containing chlorine and those not containing it. The first include sodium and potassium hypochlorite, bleach, chlorine dioxide. The second includes various salts and alkalis in combination with hydrogen peroxide, oxalic acid, acetic acid, ammonia, ozone.

Active oxygen-based bleaches work great on aged wood, but are less effective against staining fungi. They do not have an unpleasant odor (if they do not contain ammonia), do not require thorough rinsing with water after treatment, but their working solution is viable for a short period of time.

In addition to the main components, the bleach contains substances such as stabilizers that slow down the decomposition of bleaching components, fungicidal additives, agents that improve the penetration of the solution into wood, catalysts, thickeners and surfactants ( detergents). Fungicidal additives serve to protect against fungi and mold after bleaching; agents and catalysts do not themselves participate in bleaching, but help the bleaching agent penetrate the pigments. Thickeners allow you to apply a larger layer of bleaching composition to the surface of the affected wood, and surfactants help wash away contaminants.

How is wood bleached?

When wood is treated with bleaches, the pigment bonds of lignin become discolored due to the destruction of chromophore groups and discoloration of the cells of wood-staining fungi.

When is wood bleaching necessary?

In wooden house construction, the need for bleaching may arise as a result of improper storage of the material, in warm and humid weather, or in conditions of unventilated timber.

It is impossible to plan damage to wood; it can occur at any time during construction. It is advisable to carry out bleaching immediately after detecting that the wood has been painted in an uncharacteristic color.

The need to bleach lumber usually arises for two reasons: damage to the lumber stock and damage to the lumber.

In the first case, it is possible to determine the need for bleach, but in the case of lumber, it is impossible to plan for such a need; it arises as the problem is identified.

Both builders and lumber manufacturers are among the most common users of bleach. This is sometimes explained by purely economic considerations, because the cost of blue-affected lumber is $80 per 1 m, and the cost of high-quality lumber reaches 250 euros per 1 m. However, in the case of lumber processing, it must be remembered that after planing the fact of bleaching will be obvious, since the impact of chemicals is less deep to whiten the wood throughout its entire thickness, and is about 2 mm.

Another thing is bleach treatment. finished products, for example rounded logs or joinery. The need for bleaching arises if you need to cover them with transparent compounds, lighten the overall background or remove stains. The requirements for the surface of joinery products are high, therefore the bleaching composition should not destroy the structure of the wood or impair adhesion, and the action of the composition should be gentle in order to preserve the natural pattern.

What is required from wood bleaches?

Bleaching agents used in sawmilling, home construction and carpentry must have certain necessary properties. The composition should not destroy wood. Should be easy to prepare and apply.

Of course, the natural color of the wood must be preserved. TO necessary properties This also includes maintaining the possibility of applying tinting coatings, adhesives and transport, as well as preservative antiseptics after bleaching. The bleach must be safe.

It should be taken into account that bleaching is not a protective measure and the affected wood, after restoration of its natural color, can be again affected by wood-staining fungi.

Regina BUDARINA

All photos from the article

It is believed that white tree in internal and exterior decoration home looks most attractive. Among other things, the predominance of light colors in the interior increases the visual volume of the room; light lining external cladding will make the structure more elegant and weightless.

Meanwhile, with prolonged service, the wood darkens. We will try to figure out how this problem can be solved.

Causes of darkening

There are several of them.

• Ultraviolet. Under its influence, the process of wood fermentation occurs; as a result, in bright light it gradually acquires an increasingly rich shade of yellow-brown.

It’s curious: this feature does not apply to all types of wood.
Pine, whose low price makes it the most popular, does turn yellow quickly in the light; but teak and walnut, on the contrary, fade.

• Humidity fluctuations. Raw wood usually appears darker. The mechanism here is simple and obvious: dry wood is a honeycomb structure with an abundance of cavities, the air bubbles in which provide bright hues. When moistened, the cavities are filled with water, which has a completely different refractive index of light.
• Finally, with prolonged moisture, wood varieties that are not resistant to decay become victims of fungi.. Mold partially destroys organic matter; its spores and waste products not only cause the surface to darken, but also form untidy sagging and stains on it.

Prevention

Knowing the reasons for darkening, making white wood as durable as possible and preventing discoloration is not too difficult.

Antiseptic treatment

It will prevent the development of mold fungi in the wood.

It is worth clarifying: most of Modern antiseptic primers for wood combine several functions.
They prevent fungal infection, successfully fight wood-boring insects and reduce the flammability of wood.

Paint cannot always cover uneven wood color.

Even healthy wood can have multi-colored spots - this is a sign of uneven distribution of natural pigment. What can we say about wood that has been stored for years and has darkened when exposed to air? Sometimes it is necessary to bleach the wood and in order to give it a completely White color. Bleaching is carried out immediately before painting the wood.

Bleaching agents include hydrogen peroxide, oxalic acid, bleach and titanium peroxide, with hydrogen peroxide, oxalic acid and all-purpose fabric bleach being the most effective and readily available.

Each solution is prepared at the rate of 50 ml per 1 m2 of surface. But they all must have a certain consistency.

A 10-12% solution of hydrogen peroxide is suitable for bleaching wood. You should not increase the proportion of overhydrol - this can destroy the top layers of wood. Better add ammonia in proportion: for 10 parts of solution, 1 part of alcohol. In order for the surface to be evenly discolored, apply the solution to the wood with a cotton swab or a regular brush 3-4 times every 10-15 minutes. The effect will not be noticeable immediately, but only after a day or two. After the wood has acquired desired color, the solution is washed off with warm water.

Oxalic acid is more toxic than hydrogen peroxide, so it is used only in the form of an aqueous 5-10% solution. The bleaching process with oxalic acid includes several stages. First, prepare a 10% solution of oxalic acid and a 20% solution of sodium hydrosulfite. The surface is treated with a salt solution, after which oxalic acid is immediately applied, mixing the two components on the surface. After no more than 5 minutes, the solutions are removed by washing the product with warm water.

Oak is practically not amenable to bleaching with hydrogen peroxide. When kept in this substance for a long time, its wood only acquires a greenish tint. This reagent is effectively used for bleaching such breeds as Walnut, birch and beech. Before applying a 30% hydrogen peroxide solution, the veneer or solid wood is moistened warm, slightly dried and treated with a 10% ammonia solution. A mixture of 20% solutions of hydrogen peroxide and ammonia in a ratio of 1:10 is recommended for bleaching ash and birch.

Light wood species - linden, birch, maple, poplar - are bleached with a solution of oxalic acid (1.5-6 ml per 100 ml boiled water). To neutralize the acid remaining on the product, use the following composition: 15 g of bleach, 3 g of soda ash, 100 ml of water. First in hot water dissolve the soda, and after the resulting solution has cooled, add bleach to it. Treatment with this composition helps not only to bleach the wood, but also to raise the pile.

After applying all the solutions, the part is thoroughly washed with water and dried.

To bleach oak veneer, oxalic acid is used, less often - a 5% solution of citric or acetic acid. Accelerated whitening can be done using an aqueous solution that contains 2% sulfuric acid, 1.5% oxalic acid and 2.5% sodium peroxide.

Sometimes, when bleached, wood of some species acquires rather unexpected shades. Thus, walnut, which has a contrasting texture, becomes grayish-blue or pink, and oak becomes greenish.