Craft Smart® Acid and Glue Brush Pack, 6 Pc

6 (six) is the natural number following 5 and preceding 7. It is a composite number and the smallest perfect number.

An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen ion, H⁺), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid.

The first category of acids are the proton donors, or Brønsted–Lowry acids. In the special case of aqueous solutions, proton donors form the hydronium ion H₃O⁺ and are known as Arrhenius acids. Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents. A Brønsted or Arrhenius acid usually contains a hydrogen atom bonded to a chemical structure that is still energetically favorable after loss of H⁺.

Aqueous Arrhenius acids have characteristic properties that provide a practical description of an acid. Acids form aqueous solutions with a sour taste, can turn blue litmus red, and react with bases and certain metals (like calcium) to form salts. The word acid is derived from the Latin acidus, meaning 'sour'. An aqueous solution of an acid has a pH less than 7 and is colloquially also referred to as "acid" (as in "dissolved in acid"), while the strict definition refers only to the solute. A lower pH means a higher acidity, and thus a higher concentration of positive hydrogen ions in the solution. Chemicals or substances having the property of an acid are said to be acidic.

Common aqueous acids include hydrochloric acid (a solution of hydrogen chloride that is found in gastric acid in the stomach and activates digestive enzymes), acetic acid (vinegar is a dilute aqueous solution of this liquid), sulfuric acid (used in car batteries), and citric acid (found in citrus fruits). As these examples show, acids (in the colloquial sense) can be solutions or pure substances, and can be derived from acids (in the strict sense) that are solids, liquids, or gases. Strong acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid.

The second category of acids are Lewis acids, which form a covalent bond with an electron pair. An example is boron trifluoride (BF₃), whose boron atom has a vacant orbital that can form a covalent bond by sharing a lone pair of electrons on an atom in a base, for example the nitrogen atom in ammonia (NH₃). Lewis considered this as a generalization of the Brønsted definition, so that an acid is a chemical species that accepts electron pairs either directly or by releasing protons (H⁺) into the solution, which then accept electron pairs. Hydrogen chloride, acetic acid, and most other Brønsted–Lowry acids cannot form a covalent bond with an electron pair, however, and are therefore not Lewis acids. Conversely, many Lewis acids are not Arrhenius or Brønsted–Lowry acids. In modern terminology, an acid is implicitly a Brønsted acid and not a Lewis acid, since chemists almost always refer to a Lewis acid explicitly as such.

A brush is a common tool with bristles, wire or other filaments. It generally consists of a handle or block to which filaments are affixed in either a parallel or perpendicular orientation, depending on the way the brush is to be gripped during use. The material of both the block and bristles or filaments is chosen to withstand hazards of its intended use, such as corrosive chemicals, heat or abrasion. It is used for cleaning, grooming hair, make up, painting, surface finishing and for many other purposes. It is one of the most basic and versatile tools in use today, and the average household may contain several dozen varieties.

A craft or trade is a pastime or an occupation that requires particular skills and knowledge of skilled work. In a historical sense, particularly the Middle Ages and earlier, the term is usually applied to people occupied in small scale production of goods, or their maintenance, for example by tinkers. The traditional term craftsman is nowadays often replaced by artisan and by craftsperson.

Historically, the more specialized crafts with high-value products tended to concentrate in urban centers and their practitioners formed guilds. The skill required by their professions and the need to be permanently involved in the exchange of goods often demanded a higher level of education, and craftspeople were usually in a more privileged position than the peasantry in societal hierarchy. The households of artisans were not as self-sufficient as those of people engaged in agricultural work, and therefore had to rely on the exchange of goods. Some crafts, especially in areas such as pottery, woodworking, and various stages of textile production, could be practiced on a part-time basis by those also working in agriculture, and often formed part of village life.

When an apprentice finished their apprenticeship, they became a journeyman searching for a place to set up their own shop and make a living. After setting up their own shop, they could then call themselves a master of their craft.

This stepwise approach to mastery of a craft, which includes the attainment of some education and skill, has survived in some countries to the present day. But crafts have undergone deep structural changes since and during the era of the Industrial Revolution. The mass production of goods by large-scale industry has limited crafts to market segments in which industry's modes of functioning or its mass-produced goods do not satisfy the preferences of potential buyers. As an outcome of these changes, craftspeople today increasingly make use of semi-finished components or materials and adapt these to their customers' requirements or demands. Thus, they participate in a certain division of labour between industry and craft.

Smart may refer to a high level of intelligence or "street smarts".

"Smart" or SMART may also refer to the following.