Why does blotting paper absorb ink?

If you have used a dip pen or a fountain pen, blotting papers are undoubtedly handy. It is an extremely absorbent paper used to suck up excess liquid material, such as oil or ink, from an object’s or writing surface. Through that, you will no longer have to wait until the ink dries on the page, especially when you need to turn it or pick up the paper you just wrote with your hands. But, how does blotting paper actually work?

A blotting paper is pretty porous. It has tiny spaces or holes, which serve as capillary tubes. Capillary action, or the natural tendency of liquid to ease surface tension, results in the absorption of the ink. When a capillary tube is plunged in any liquid, the fluid enters into these tubes up to a level higher than outside of it.

Often, blotting papers are made of cellulose, usually from wood, straw, or cotton linter, allowing the presence of the microscopic holes. As it comes in contact with an aqueous solution, the liquid is drawn into these cavities. Once filled in, it moves to the next capillary spreading the ink into the sheet.

You can also observe capillary action when you place a narrow into a glass of water. Try to check the water’s level in straw and the glass. You can notice that the level of the water inside the straw has risen up higher than that of the glass’. That scenario is also brought by capillary action, seemingly defying gravity. It is the unique property of water to move through the surface of another material, despite the presence of different forces.

Capillary action occurs in many instances in our daily living. It is responsible for why a paper towel can suck up spilled milk or juice or why you are able to dry yourself quickly after a bath. That is capillary action as the liquid form climbs up to the paper towel, dragging all the water molecules.

Trees and plants also use capillary action to survive. They place down roots deep in the ground, which are capable of transporting water from the soil into the plant. Dissolved nutrients are present in the water on the soil. The roots then absorb the water and start rising up to the plant’s tissue.

Capillary action works by bringing water to the roots. However, it is only the initial action as it can only drag water to a certain extent. To transport water up all the leaves and branches, the plant’s mechanism, using the adhesive and cohesive forces, works to bring water up to the outlying leaf.

But today, blotting paper is more commonly used in cosmetics to absorb excess oil from the face. It is made from ingredients, such as cotton, rice, and flax seeds. They are widely marketed and sold by different cosmetic brands across the globe. Often they are also dyed to make them more visually-enticing for consumer appeal. Others are dusted with minerals and salicylic acid to prevent further formation of acne and other blemishes on the skin. These blotting sheets used the same magic of capillary action to soak up excess sebum, making it less shiny and more matte.

More Readings:

Blotting paper (Wikipedia)

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