Bright Stock

High-viscosity residual stock for body & tack

Bright stock is the heavy residual base oil left after deasphalting and solvent refining of vacuum residue, and it behaves nothing like a neutral. BS150 (the common export grade, sometimes written BS150 or SN650-plus) runs roughly 28–32 cSt at 100°C and 400–500 cSt at 40°C, viscosity index ≥ 90, flash point ≥ 280°C COC and pour point around -6 to -9°C. Its ASTM colour is the giveaway: 6.5–8.0, deep amber to brown, because the high-molecular-weight aromatic and residual fraction that gives it viscosity also gives it colour. Nobody buys bright stock for colour — they buy it for body, film strength, tack and high-temperature viscosity retention, and it is almost exclusively a Group I product because hydroprocessing cannot economically make its viscosity range.

You reach for bright stock when SN500 has run out of road: above roughly 12 cSt at 100°C, no amount of heavy neutral gets you to an SAE 50 or 60 monograde, an ISO 320/460/680 industrial gear oil, or a marine cylinder oil. It is the viscosity-building component in grease manufacture, the tack and adhesion component in open-gear, chain and way lubricants, and the body in heavy-duty gear oils and rock-drill oils. The trade-off is unavoidable: you gain viscosity and film strength, you accept dark colour and higher pour. CBIL brokers Group I bright stock from Gulf, South Korean and Singaporean refiners with COA and SGS verification of viscosity at 40°C and 100°C, VI, flash, pour and ASTM colour. Because global Group I capacity is contracting and bright stock is a by-product of it, availability is structurally tighter than for neutrals — supply is arranged in 24 MT flexitanks, ISO tanks and new steel drums on FOB, CFR and CIF terms, and forward positions are worth taking.