Defects in Vegetable Tanned Leather

Here are some causes of visual defects and irregularities in vegetable tanned leather seen at the tannery.

Stains on pelts

• Black Stains
  • Iron stains, chiefly caused during transferring (iron rails, drip water), appearing after sulfide liming (iron sulfide)
  • Sodium sulfide containing water
• Blue and Red Stains
  • Damages caused in curing, salt stains, germ caused by microorganisms

Stains on leather

• Brown Stains
  • Sludgy extracts
  • Flocculations in the suspenders, which deposit in the grain
  • Air stains
  • Contact Stains (Suspender liquors)
  • Tannin migrated to the surface
  • Tannins stains before coloring
  • Burnt areas, caused, e.g., by scorching
• Black Stains
  • Iron stains caused in splitting or shaving or by drip water etc.
• Greenish Stains
  • Copper stains caused by pipes or fittings
  • Sumac stains (chlorophyll)
• Grey-Brown Stains
  • Lime stains (lime blasts) caused by exposure to air, use of hard water for washing and rinsing, lime liquor prepared with fresh water
• Dark Stains, (especially in the flanks and shaved areas)
  • Scud not properly removed
• Pale Stains, round
  • Stains caused by pools of tan or bleach liquors
• Pale Stains, oblong
  • Abrasions, especially those caused by drumming
• Pale Pinholes (pits)
  • Damages caused by curing: pits caused by overbating
• Pale Spots
  • Bleaching materials not completely dissolved before addition
• Greyish Leather Shade
  • Tan liquors containing iron; concrete pits, fittings, suspension frames
  • Iron content of plant water too high, possibly caused only by rusty pipe line or condensing water containing grease
• White spue (removable with water)
  • Salt spue, (sodium sulfate, magnesium sulfate, common salt) due to sole leather seasons or to old, worked down liquors; insufficient steeping or rinsing
• White spue (not removable with water)
  • Fatty spue, usually consisting of free fatty acids, but with solvents; melts in the heat; and sometimes of higher fatty alcohols
• Leathers match test failures
  • Fat liquored too acid or unsuitable fat liquoring agents were used. May also be caused by fat splitting microorganisms
• Uneven penetration, (untanned middle)
  • Too intensive coloring (case-hardening)
  • Sludge layer in the pores
  • Excessively exhausted liquors
• Poor and loose flanks
  • Poor raw material
  • Lime too old
  • Bating bath too strong or too warm
  • Excessive straining

Grain faults

• Loose Grain
  • Poorly cured raw material
  • Excessively stressed by prolonged soaking, liming or bating
  • rummed too long in short liquors
  • Overstrained by swelling
• High Grain
  • Excessive initial swelling in the lime
  • Coloring liquor too acid
• Cracked Grain
  • Careless handling of the raw hides
  • Careless handling of excessively swollen pelts
  • Excessive pressure of sammying and setting out machines etc.
• Pebbled Grain
  • Prolonged drumming
  • Liquor too short
  • Rate of revolution too high
• Drawn Grain
  • Coloring in liquors that are too fresh, too acid, too strong or too warm.
  • Liquor too short
  • Rate of revolution too high.
  • With combination- tanned leathers, tanning liquors too strongly absorbed