Fish Products and Byproducts Technology

Unit 10 - Fish By- products

10.4. Pearl Essence
Pearl essence is the suspension of crystalline guanine in water or organic solvent. Guanine is an iridescent material found in the epidermal layers and scales of most pelagic species of fish like oil sardine, mackerel, herring etc. When guanine particles are deposited on the inside surface of solid beads, an optical effect similar to that of real pearl is obtained.
Process
Freshly removed scales are collected and washed to obtain adhering foreign matter. Scale can be preserved in 10- 15% brine which is later drained off and scales are squeezed in muslin cloth bag and compressed. It can be stored at 0° C for several weeks without getting them dry. Pearl essence can be prepared as aqueous and no – aqueous suspension
Aqueous suspension can be prepared by agitating washed scales with water containing little ammonia. The mixture is then passed through a strainer. The pearly substance present as a suspension in the liquor is purified by settling in a cool atmosphere. Guanine settles and supernatant is decanted and replaced with fresh ammoniacal water. The process is repeated several times and 0.3% salicylic acid is used as preservative.
Non- aqueous suspension can be made by suspending it in organic solvents like acetone, amyl acetate, chloroform or acetic acid. It is presented in a form of thick paste of crystals suspended in viscous liquor of cellulose of amyl acetate.

Uses

• In the manufacture of artificial pearls
• It is used on diverse articles such as shoe, pencil, fishing rod and spectacle frame