A colored lead for writing, drawing and coloring implements, more particularly erasable, sintered colored lead, or to a colored chalk, more particularly erasable, sintered colored chalk, having a sintered lead or chalk base body which is formed from a lead or chalk base material containing at least one binder with a proportion of from 1 to 25% by weight and at least one filler with a proportion of from 25 to 99% by weight. The sintered lead or chalk base body is impregnated with at least one colorant and at least one lubricant.

A colored lead for writing, drawing and coloring implements, more particularly erasable, sintered colored lead, or to a colored chalk, more particularly erasable, sintered colored chalk, having a sintered lead or chalk base body which is formed from a lead or chalk base material containing at least one binder with a proportion of from 1 to 25% by weight and at least one filler with a proportion of from 25 to 99% by weight. The sintered lead or chalk base body is impregnated with at least one colorant and at least one lubricant.

The present invention provides writing compositions that are capable of being erased or changed in color chemically. The present invention also provides erasing media for erasing or changing the color of marks produced with the writing compositions, as well as writing systems and incorporating the erasing media and the writing compositions. The present invention further provides writing instruments produced using the writing compositions.

The present invention provides writing compositions that are capable of being erased or changed in color chemically. The present invention also provides erasing media for erasing or changing the color of marks produced with the writing compositions, as well as writing systems and incorporating the erasing media and the writing compositions. The present invention further provides writing instruments produced using the writing compositions.

This disclosure describes a process for preparing silica-coated calcium carbonate particles, involving the steps of preparing an aqueous carbonate slurry containing calcium carbonate particles, adding at least one silicate composition to the aqueous carbonate slurry to obtain a carbonate-silicate slurry, lowering a pH of the carbonate-silicate slurry by adding at least one acidic compound to obtain a pH-adjusted slurry containing the silica-coated calcium carbonate particles, and isolating the silica-coated calcium carbonate particlesin which at the adding of the acidic compound is controlled such that a final pH of the pH-adjusted slurry ranges from about 7 to about 10, and the silica-coated calcium carbonate particles include a porous coating having an average pore diameter ranging from 2 nm to 50 nm. This disclosure also describes articles and compositions containing the silica-coated calcium carbonate particles, as well as hollow silica spheres formed from the silica-coated calcium carbonate particles.

This disclosure describes a process for preparing silica-coated calcium carbonate particles, involving the steps of preparing an aqueous carbonate slurry containing calcium carbonate particles, adding at least one silicate composition to the aqueous carbonate slurry to obtain a carbonate-silicate slurry, lowering a pH of the carbonate-silicate slurry by adding at least one acidic compound to obtain a pH-adjusted slurry containing the silica-coated calcium carbonate particles, and isolating the silica-coated calcium carbonate particlesin which at the adding of the acidic compound is controlled such that a final pH of the pH-adjusted slurry ranges from about 7 to about 10, and the silica-coated calcium carbonate particles include a porous coating having an average pore diameter ranging from 2 nm to 50 nm. This disclosure also describes articles and compositions containing the silica-coated calcium carbonate particles, as well as hollow silica spheres formed from the silica-coated calcium carbonate particles.

A pencil lead and a pencil containing the pencil lead wherein the pencil lead is polymer-based, extrudable, non-expanded, non-calcined and comprises graphite, of which 25% to 100% by weight or 50% to 100% by weight of the graphite, in relation to the total weight of the graphite, is expanded graphite.

A pencil lead and a pencil containing the pencil lead wherein the pencil lead is polymer-based, extrudable, non-expanded, non-calcined and comprises graphite, of which 25% to 100% by weight or 50% to 100% by weight of the graphite, in relation to the total weight of the graphite, is expanded graphite.

A method for releasing impurities from a calcium-based mineral is described. The method comprises reacting a calcium-based mineral containing impurities with an aqueous solution of one or more ionic salts at a temperature of approximately 85 C. or above, wherein at least one of the calcium-based mineral and the one or more ionic salts comprises sulphate and at least one of the calcium-based mineral and the one or more ionic salts comprises ammonium, and wherein the concentration of the solution is approximately 25% or higher mass fraction, such that double salt crystals are formed and impurities are released. The method further comprises separating the double salt crystals from the impurities. Various products of the process are also described.

A method for releasing impurities from a calcium-based mineral is described. The method comprises reacting a calcium-based mineral containing impurities with an aqueous solution of one or more ionic salts at a temperature of approximately 85 C. or above, wherein at least one of the calcium-based mineral and the one or more ionic salts comprises sulphate and at least one of the calcium-based mineral and the one or more ionic salts comprises ammonium, and wherein the concentration of the solution is approximately 25% or higher mass fraction, such that double salt crystals are formed and impurities are released. The method further comprises separating the double salt crystals from the impurities. Various products of the process are also described.