" " wisno wood furniture finishing: Wood bleach in the furniture finishing

Monday, March 15, 2010

Wood bleach in the furniture finishing

Wood bleach

Bleaching the wood is a process that sometime cannot be avoided in the finishing process. Some time we meet the condition when the final finishing color required  is lighter than the wood base color. When we deal with the designer, some time they ask something that difficult to be achieved (illogical). Some peoples want to want to get light color finish the dark wood that have good grain. The crotch mahogany, teak, walnut or rosewood are examples of the types of wood that has a strong and good pattern grain with dark base color. To make the light finishing color for those wood we need to light up their wood base color.  In this case we can bleach the wood to whiten the wood base color. The bleaching process to the wood is actually similar to the bleaching process in the other things such as bleaching the clothes or the hair. But  to bleach the wood we need a quite strong chemical the the bleaching for the hair and clothes. 

Materials for bleaching.
The chemical used for bleaching process is known as bleaching agent. The bleaching agents that mostly used in wood industry is the hydrogen peroxide or H2O2. In the store this material is commonly known as the material A. Hydrogen peroxide actually can be used alone to bleach the wood, but usually the result is rather yellow or brown since the acidity of the chemical. If we want a real whiter color, then we require other chemicals for neutralizing the acid of this material. The material used is the alkaline solution. The material that is commonly used is: sodium hydroxide or ammonium hydroxide is also commonly referred as the B material.
Materials A and B will react when they are mixed, then the mixing of those two materials must be done just before the bleaching materials is applied to the wood surfaces. The mixed of A and B material will not effective to bleach anymore after the reaction has finished and stopped. An easier way to do is to apply interchangeably. Material B is applied first to the surface of the wood and then followed later the material A then is applied to the surface of the wood which is still wet with material B. By this way there is a reaction oxidation and neutralization in the same time.
Some peoples use the soda ash powder (calcium bicarbonate) about 5% of mixed directly into the solution of hydrogen peroxide. 
The 2 component bleaching will give whiter color then the hydrogen peroxide alone.
Actually there are also some other materials which also could be used for bleaching such as: oxalic acid and chlorine. Oxalic acid is more widely used to remove the blue stain in wood. Both materials are relatively more secure than with hydrogen peroxide, but the bleaching power is not as strong as the hydrogen peroxide.

Bleaching process.

Bleaching materials can be applied by brush, rag or spray. The reactions in the bleaching process would be better if it is put under heat. The maximum result will be obtained if the wood is put outside in the sunny day. If the results obtained are less white, then the process can be repeated again to obtain the desired results. After bleaching process the wood has to wait until the chemical reaction is completed before go to the next process. We can wash the bleaching chemical to make sure that the surface is clean. The hydrogen peroxide solution should be washed with vinegar, while the oxalic acid is washed with baking soda, and the chlorine is washed with water.

  Crotch mahogany has a strong red color

Bleaching chemical is applied on the crotch mahogany veneer

 The white crotch mahogany after have been bleached

The thing need to be considered in the bleaching process:
  •  The process of bleaching must be done carefully, bleaching substances are hazardous chemicals. Bleaching process should be conducted in open space, or in a room that has good air circulation. Bleaching liquid is a toxic material, it will hurt if exposed to the skin or limbs. Its fumes will irritate the respiratory if be inhaled by humans. Always use protective equipment, special clothes and gloves to protect the body and respirator to protect the respiratory organ.
  •  Make sure that the bleaching process is completely dry before you continue with the next process. The remnants of bleaching material will cause many problems in the finishing process.
  • The process of bleaching will make the wood surface becomes rough because of the wooden fibers are rising due to the process of wetting the wood. After the bleaching we should re sand the wood surface. The sanding should be done properly. It has to be sufficient to produce a smooth surface, but not too much since it will eliminate the white surface layer and the dark colored wood will appear again.
  •  For laminate wood or veneer, bleaching should be done carefully, because the bleaching chemical is a water solution that will wet the wood, make sure the glue is strong enough. If the glue used is not strong enough it could result of loose veneer or damage the lamination of the wood..


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