What is the usual composition of acid etch?

Explanation:acid etching  

etching

the cutting of a hard surface such as metal or glass by a corrosive chemical, usually an acid, in order to create a design.

etching  - etching of dental enamel with an acid in order to roughen the surface, increase retention of resin sealant, and promote mechanical retention.

acid etching

microscopic roughening of dental enamel with an acid (usually phosphoric acid) to remove the smear layer and open enamel tubules, increase retention of resin sealant, and promote mechanical retention.

acid etching Dentistry

The application of a weak acid—e.g., 30% phosphoric acid—to the surface of enamel to roughen the surface of a tooth before bonding a resin or veneer; acid etching increases mechanical retention, cleans the enamel and improves the wetting of resins. See Cosmetic dentistry.

explanation: it gains negative electrons, therefore becoming negatively charged. as charge cannot be created, nor destroyed, only transferred, this leaves the wool positive. now that they have opposite charges, the two items attract.