A rechrome fatliquor is judged on chrome in the bath and on fibre opening. Judging it only by final hand misses the reason it was added.
A stage, not a product nickname
Tanners say “softener” for every oil. In rechrome the oil has to live with chrome salts. Esteem’s sulfited fish-oil blend is one grade described for that bath and for later dye-house stages. A cationic chrome-tannage lubricant is another. They are not substitutes.
Write the stage on the request. A sample chosen for white nappa lightfastness is the wrong rechrome oil, and a rechrome oil is the wrong sole softener for pastel aniline.
What to measure
Residual chrome and a cut-section of fibre openness tell you if the rechrome oil worked. Hand after staking tells you about the later fatliquor. Mixing the two conclusions leads to overfatliquoring and greasy grain.
Float and temperature from the product notes matter. An oil that exhausts in a small rechrome float can sit on the grain in a long dye-house float if the offer is copied across.
How it sits with syntans
Liquid and powder syntans change how later oil penetrates. If you change the retan and the rechrome oil together, you will not know which one opened the leather.
Keep beam-house degreasing in the story. Natural fat left in the hide still causes chrome soaps that look like a fatliquor failure.
| Stage | Fatliquor job | Do not expect |
|---|---|---|
| Rechrome | Exhaustion and opening | Final garment hand |
| Retan | Fibre opening in stages | Dye levelness by itself |
| Main fatliquor | Cross-section softness | Chrome fixation |
| Top fatliquor | Surface handle | A fix for poor rechrome |
Chrome fixation is a pH and complex story
Chrome tannage works because chromium(III) forms complexes with collagen carboxyl groups as the pH is raised. Basification drives that fixation. Residual chrome in the float is unfixed chrome. A fatliquor added in rechrome does not create new binding sites. It changes wetting, fibre separation, and sometimes the way the chrome liquor is distributed through a tight hide.
Sulfited oils carry sulfate and sulfonate groups, so they are anionic and can live in an acidic chrome bath without immediately breaking. A cationic chrome-tannage lubricant is the other published route. Mixing the two in one bath is an ionic clash, not a stronger rechrome.
Fibre opening versus final hand
Collagen fibre bundles that are still stuck together feel tinny even after a generous main fatliquor. Oil offered while the fibre is being rechromed can separate those bundles early. That is opening. Softness after staking is a later result of how much oil is in the cross-section and how the retan fills the voids.
Judging the rechrome oil by the crust hand therefore mis-assigns the result. A hard crust can mean a tight retan, a low main offer, or a rechrome that never opened the centre. A greasy grain can mean the rechrome percentage was repeated in the main bath. Measure residual chrome and a cut section before you change the garment offer.
What the float is doing
A small, warm rechrome float exhausts both chrome and a compatible oil. A long, cooler float leaves more of both in the liquor and gives the oil time to cream onto the grain. Temperature also changes the emulsion. A sulfited emulsion that is fine at the rechrome temperature can coarsen if the bath is allowed to cool with the hides still in it.
Natural fat that survived the beamhouse forms chrome soaps. Those soaps look like spew or uneven oil and are not fixed by raising the rechrome fatliquor. Degreasing belongs in the brief next to the chrome offer, the float, and the temperature.
How to Specify with Esteem
- State that the stage is rechrome, not the dye-house main offer.
- Give chrome offer, float, and temperature.
- Record residual chrome if you measure it.
- Keep the later main fatliquor as a separate line.
- Do not scale a rechrome percentage up to garment softness levels without a new trial.
The sulfited-oil fatliquor notes on fatliquors mention rechroming, chrome exhaustion, and softness. Read them before copying a main-fatliquor percentage.