Composite colored particles may include resin particles carrying a positive electric charge on particle surfaces and dye-containing particles carrying a negative electric charge on particle surfaces, the resin particles and the dye-containing particles forming a composite through Coulomb force. A water-based ink composition may include such composite colored particles dispersed in a water-based medium. A writing instrument may contain the water-based ink composition. A method of producing such composite colored particles may include forming a composite by mixing a resin emulsion containing resin particles carrying a positive electric charge on particle surfaces and a colored resin dispersion containing dye-containing particles carrying a negative electric charge on particle surfaces.

Composite colored particles may include resin particles carrying a positive electric charge on particle surfaces and dye-containing particles carrying a negative electric charge on particle surfaces, the resin particles and the dye-containing particles forming a composite through Coulomb force. A water-based ink composition may include such composite colored particles dispersed in a water-based medium. A writing instrument may contain the water-based ink composition. A method of producing such composite colored particles may include forming a composite by mixing a resin emulsion containing resin particles carrying a positive electric charge on particle surfaces and a colored resin dispersion containing dye-containing particles carrying a negative electric charge on particle surfaces.

Reverse photochromic ink formulations containing encapsulated reverse photochromic colorant, methods of erasing reverse photochromic ink formulations including encapsulated reverse photochromic colorants by exposing them to UV light, and writing instruments including a writing tip portion connected to a light-shielding tubular member or refill and a reverse photochromic ink formulation including encapsulated reverse photochromic colorant are provided herein.

Reverse photochromic ink formulations containing encapsulated reverse photochromic colorant, methods of erasing reverse photochromic ink formulations including encapsulated reverse photochromic colorants by exposing them to UV light, and writing instruments including a writing tip portion connected to a light-shielding tubular member or refill and a reverse photochromic ink formulation including encapsulated reverse photochromic colorant are provided herein.

Reverse photochromic ink formulations containing at least one reverse photochromic colorant, methods of erasing reverse photochromic ink formulations by exposing them to UV light, and writing instruments including a writing tip portion connected to a light-shielding tubular member or refill and a reverse photochromic ink formulation are provided herein.

Reverse photochromic ink formulations containing at least one reverse photochromic colorant, methods of erasing reverse photochromic ink formulations by exposing them to UV light, and writing instruments including a writing tip portion connected to a light-shielding tubular member or refill and a reverse photochromic ink formulation are provided herein.

Dry erase ink formulations containing a resin, a pre-assembled colorant, and a solvent, wherein the dry erase ink formulation has a surface tension of at least 25 dynes per centimeter, and writing instruments including a dry erase ink formulation are provided herein.

Dry erase ink formulations containing a resin, a pre-assembled colorant, and a solvent, wherein the dry erase ink formulation has a surface tension of at least 25 dynes per centimeter, and writing instruments including a dry erase ink formulation are provided herein.

A marking composition may include an aqueous carrier and thermochromic capsules. The thermochromic capsules may include a leuco dye, an activator, and a temperature regulator. The thermochromic capsules may have a volume average size effective to resist temperature-mediated discoloration at a temperature of at least up to 40° C. by dissipating heat. In some embodiments, the marking composition marks a substrate with a substantially erasable mark, for example, in response to frictional contact with an eraser.

A marking composition may include an aqueous carrier and thermochromic capsules. The thermochromic capsules may include a leuco dye, an activator, and a temperature regulator. The thermochromic capsules may have a volume average size effective to resist temperature-mediated discoloration at a temperature of at least up to 40° C. by dissipating heat. In some embodiments, the marking composition marks a substrate with a substantially erasable mark, for example, in response to frictional contact with an eraser.