which chemical is used for changing the colour of the paper?
818017
Generally, a dye. You need to be more specific. What paper? What colour?
196165
NaHSO4 itself is acidic, so the solution's color should be yellow due to the bromcresol green being in the presence of acid
317548
You are confusing emissive mixing with subtractive mixing. When dealing with pigments, one customarily uses the colors Cyan, Magenta, and Yellow as primary colors. This is because you are actually dealing with a subtractive spectrum. The colors of the pigments are the part of the spectrum that is not absorbed by the material, so mixing them is not an additive procedure, but a subtractive procedure. Mixing all of the three colors above will not get you white, but (in a perfect world) will subtract every color from being reflected, giving you black, the absence of photons. In the real world, the pigments are imperfect and you actually get a murky dark greenish color, which is why an independent black ink is added to printing processes (CMYK).\nRed, Green and Blue are primary for the emissive spectrum, these are used for mixing colors of pure light (ie., CRTs and LCDs). Mixing all of these colors (use red, green, and blue filters in front of white lights) will get you white, as it should. See the article below for more detail.
726521
You can get putty like ones from art shops that remove dark HB and pretty much destroy anything apart from the pressure on the paper. they need to be cleaned a lot but can be molded to an easy shape and are dabbed rather than rubbed which means less white flakes and little paper ripping.
609106
c2s art paper - means coated on two sides. This is used on high quality printing for example in museums, etc.  The paper is coated on both sides for photo quality printing, and it is compatible with both pigment and dye inks.\n\nHope this helps.\nGood Luck.
949044
1) put them into the solution of bromine, the substance which makes the solution lose its colour is NaI\n2NaI + Br2 => 2NaBr + I2\n2) dissolve them in water, barium sulfate is the only one which cannot be dissolved in water\n3) Na2CO3 + 2HCl => 2NaCl + H2O + CO2\nNaHCO3 + HCl => NaCl + H2O + CO2
316837
Actually, I believe you would need to change the color of the text you are trying to print.
11100
Use a black sharpie...works like a charm!
475249
Paper is made from wood, which is made up mainly of white cellulose. Wood also has a lot of a dark substance in it called lignin, which ends up in the paper, too, along with the cellulose. The exposure of lignin to air and sunlight is what turns paper yellow.\n\nLignin makes wood stiff and trees stand upright. You could say it acts as a glue to bind the cellulose fibers together. It is a polymer, a substance that is formed by the joining of simpler molecules into giant molecules that act differently than the smaller molecules did. Dr. Hou-Min Chang, a professor of wood and paper science at N.C. State University in Raleigh, N.C., compares lignin to the concrete used in buildings, with cellulose as the steel frame. Without lignin, Chang says, a tree could only grow to be about 6 feet tall. Lignin also helps protect the wood from pests and other damage.\n\nNewsprint, which must be produced as economically as possible, has more lignin in it than finer papers. At the mill, the wood that will be turned into newsprint is ground up, lignin and all.\n\nPaper manufacturers utilize the benefits of lignin in some types of paper, though. Brown kraft paper, the dark brown paper used in grocery store bags, and cardboard are stiff and sturdy because they have more lignin in them, and because those kinds of paper aren't treated with bleaching chemicals. It doesn't matter how dark they are because the printing on them is limited.\n\nTo make a fine white paper, the mill puts the wood through a chemical solvent process, which separates and discards the lignin. Pure cellulose is white, and the paper made from it will be white and will resist yellowing.\n\nLignin eventually turns paper yellow because of oxidation. That is, the lignin molecules, when exposed to oxygen in the air, begin to change and become less stable. The lignin will absorb more light, giving off a darker color. Chang says that if newsprint were kept completely out of sunlight and air, it would remain white. After only a few hours of sunlight and oxygen, however, it will start to change color.
762457
There are several ways to make paper look old, here are just a few.\n\nSpread milk all over the paper and put it in the oven at 360 degrees for a half a hour to a hour. WARNING - Keep an eye on the paper during this process in case it catches light!\n\nDab the edges of the paper with water, then use a lighter or candle to char the edges. \n\nMake 1 pot of dark coffee with no sugar or milk. Combine it with 5 or more teabags and then leave the coffee to settle for about 2 hours to 2 hours and a half. Then take a paintbrush and paint over the paper with the coffee and tea and then let it dry over night between 2 white pieces of paper. \n\n\nMake a pot of tea and keep it warm \nCrumble the paper up and dip it inside the tea \nUse a match to light the edges of the paper \n\n     There you go! One historic looking document!
46685
I'm not familiar with that one.  I do know, however, that you can create invisible ink with lemon juice.  Take the lemon juice, write your letter, and then when you want to read it, heat it up CAREFULLY in an oven or on a hot surface.  Perhaps the same would work with a solution of baking soda and water.
522216
Food colouring and bleach.
683604
1. water\n2. food coloring\n3. vinigure or sodium (for bubbling)\nsorry if this doesnt work\nhavnt done it in a long time
626101
methyl orange has a 95% confidence level\n\nbromcresol green is also used, and the color changes from yellow to blue\n\nMethyl Red changes colors from red to yellow
208500
Perhaps the plants transpiration processes of; photosynthesis, CO2, & nitrogen along with other conditions, ie. H2O temp., Ph level, UV length of intensity play a part of the chemical transformation of plant material to become reddish in color.  Ideally, a micro nutrient of Fe (iron) would make a difference but not certain.
647043
(NH4)SO4 is ammonium sulphate and is a base and will turn litmus paper blue and phenolphthalein pinkish\nH2CO3 is Hydrogen carbonate and will produce no change in either as it is a neutral compound in both.
926706
The chemical is called melanin...