Say whether the blue was sammed, crusted, or held wet. A standard dye-house offer assumes a wet, open substrate.
Storage changes the substrate
Wet blue loses water, the grain tightens, and any residual fat sets. A fatliquor offer copied from yesterday’s fresh pack will exhaust on the surface of today’s dry pack. The chemical did not change. The leather did.
Say how the blue was held. A trial on fresh blue does not qualify a recipe for crust that has sat for weeks.
Wetting back, then process
Rewet to a uniform cut before neutralization and dye. The multipurpose grade’s wetting-back claim is the Esteem sentence to use when that is the defect. Adding more dye to a dry centre only makes a darker ring.
If the blue is moldy or heat-damaged, wetting will not restore it. Sort that stock out of the chemical trial.
Symptoms
Neutralization after a poor rewet is uneven, so syntans and oils that follow will also be uneven. Fix the water before you fix the retan.
Record weight before and after wetting. Offers on shaved weight are meaningless if the leather was weighed dry and processed half-wet.
| Symptom | Check first | Wrong conclusion |
|---|---|---|
| Dark grain, pale centre | Rewet of the centre | Bad dye lot |
| Oil on the grain only | Substrate openness | Need more top oil |
| Fresh blue is fine | Storage history | The fatliquor drifted |
| Mold and stain | Storage, not surfactant | A stronger wetter |
Storage changes the surface
Wet blue that is sammed and stored, or that dries at the edges of a pack, loses free water. Fibres set closer together and any residual fat concentrates at the grain. Months of storage add a hydrophobic surface even when the leather was easy to wet on the day it was tanned. The dye house then sees a crust that will not wet back evenly, and the shade and the oil both go to the surface.
A wetting-back surfactant is chosen to work at the pH of the wash or the dye float, not at beamhouse pH. Nonionics and some anionics that survive mild acid and salt are the usual tools. A beamhouse sulfide wetter is the wrong sample.
Wetting back is not degreasing
If the defect is a water break that disappears in a few minutes, the leather needs a wetter. If the defect is a persistent grease spot or a chrome soap, the leather needs a degreasing step and the wetter will only move liquor around the spot. Combining both requests in one product without saying which defect you see produces a detergent that strips fat the later process wanted, or a mild wetter that leaves the spot.
Temperature helps either way. A cold wash on a dried, heavy hide does not open the centre. The wetter cannot create a float that was never given time to penetrate. State thickness and how dry the pack is.
What even wetting looks like
After the wetting-back float, a cut should show water through the section, not a wet rim and a dry centre. Only then should dye or fatliquor be added. Starting the dye in the same liquor before the centre is wet locks in a ring shade that no dispersing oil can fully repair.
Record storage time, whether the blue was wrapped or allowed to dry, the wash temperature, and the pH. A grade that wets a fresh, damp blue in ten minutes can need a different dose and time on a three-month dry edge. The specification is the dry leather you actually have.
How to Specify with Esteem
- State wet, sammed, or dry crust.
- Give storage time and temperature if known.
- Wet back before you judge a new fatliquor.
- Cut the leather after wetting to see the centre.
- Only then run the retan and dye comparison.
The multipurpose fatliquor notes excellent wetting-back properties on fatliquors. Beam-house wetting agents are the other family if the problem starts at the soak.