A turbine engineer sent me above photos and asked Khash ==> Journal or Bearing ? Which place varnishing happens first ? Needing a detailed article on it 

Khash Replied

Direct answer

The bearing is the stationary sleeve/pad/shell around it. In a hydrodynamic/plain journal bearing, the shaft journal is supported by an oil wedge, and under correct operation the shaft and bearing surfaces should be separated by an oil film, not rubbing directly. (miba.com)

But varnish does not truly “start” on either the journal or the bearing.
It starts as oil degradation products in the lubricant. Those products later deposit on metal surfaces as amber/brown varnish. In a journal-bearing assembly, the first persistent surface varnish is usually on the stationary bearing surfaces, pads, oil grooves, edges, drain areas, and low-flow/hot zones. The journal often shows the stain later as a transferred/wiped witness mark.

From the photos, I would describe this as:

“Journal surface showing varnish/thermal oil deposit, likely related to varnish formation inside the journal bearing zone.”

Not simply “bad journal” or “bad bearing” yet. The root cause is usually oil condition + bearing temperature/shear/flow condition.

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Varnishing in Journal Bearings: Where It Starts, Why It Happens, and How to Read the Marks

1. Journal vs bearing: correct terminology

A journal is the smooth cylindrical part of the rotating shaft that runs inside the bearing.

A journal bearing is the stationary support that carries radial load. It may be a sleeve bearing, plain bearing, tilting-pad journal bearing, or fluid-film bearing. In hydrodynamic operation, shaft rotation drags oil into a wedge-shaped film that supports the load and separates the shaft from the bearing surface. (miba.com)

So, in your photos:

Brown/golden marks on the rotating cylindrical shaft = journal marking.
The pads/shells/shoes around the shaft = bearing parts.

The visible stain is on the journal, but the condition should be treated as a journal-bearing lubrication varnish issue, not only a shaft-surface issue.

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2. What varnish is

Lubricating-oil varnish is a thin, sticky-to-hard film made from degraded oil and depleted additive by-products. It often appears yellow, amber, orange, reddish-brown, dark brown, or shiny glazed depending on severity and temperature history. WearCheck describes varnish as starting from oil degradation products and depleted additives, with heat, air, moisture, contamination, and catalytic wear metals contributing to formation; it can cure into a hard shiny glaze on hot or wearing surfaces.

Pall similarly describes varnish as an insoluble film deposit that forms on internal surfaces such as pipes, tanks, bearings, heat exchangers, and servo valves, with higher temperatures accelerating oil oxidation. (Pall)

That matches the color pattern in your images: amber/brown staining, glazed appearance, and banding around the shaft.

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3. Where varnishing happens first

There are three “first places” depending on what you mean.

A. Chemically, varnish starts in the oil

The earliest stage is not on the metal at all. It begins as soluble or semi-soluble oil degradation products in the circulating oil. These are sometimes called varnish precursors. They may remain dissolved until the oil loses solvency, cools, becomes saturated, or meets a surface where the deposit can plate out.

B. In the oil system, deposits often appear first in low-flow or cooler areas

Varnish precursors can settle or plate out where oil flow is slow, where temperature changes, or where the oil has long residence time. That can include tanks, return lines, coolers, filters, valve bodies, dead legs, and drain areas. WearCheck notes that varnish can form on internal machine surfaces including gears, tanks, pipework, journal bearings, control valves, and seals.

C. Inside a journal bearing, visible varnish usually appears first on the bearing/pad side

Inside the bearing itself, the stationary bearing surface usually gets the first stable deposit because it does not continuously wipe itself the way the rotating journal does. The bearing pads/shells also provide more surface area for deposit formation. STLE notes that high varnish levels may form deposits especially on journal bearing pads, and severe cases can produce elevated bearing temperature and vibration. (stle.org)

So the practical answer is:

First chemical formation: in the oil.
First stable surface deposit in the bearing area: usually bearing pads/shells, oil grooves, edges, and low-flow/hot zones.
First obvious visual mark during inspection: often the journal, because the shaft surface shows a shiny amber/brown witness band.

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4. Why the journal shows strong staining even if the bearing started it

The journal rotates at high surface speed. During normal hydrodynamic operation, it is separated from the bearing by an oil film. But if varnish begins building on the bearing pad, it can reduce clearance and disturb the oil film. WearCheck states that varnish on journal bearings can reduce operating clearance, increase wear risk, and trap dirt or wear metals.

Once clearance is reduced, several things can happen:

The oil film gets thinner.
Local temperature rises.
The bearing pad may develop a sticky/glazed deposit.
The journal wipes against contaminated oil/deposit during start-up, shutdown, slow roll, turning gear, or transient load.
The journal then receives a brown transfer mark.

That is why the shaft can look like “the problem,” while the bearing pad and oil condition may be the actual origin.

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5. Typical varnish locations in a journal bearing

In a hydrodynamic journal bearing, oil enters relatively cool, is dragged into the load zone, and leaves hotter. The most common varnish-prone areas are:

Loaded bearing pad or lower shell.
This area sees the highest load and high oil-film shear.

Minimum-film-thickness region.
This is where the film is thinnest, temperature is high, and the lubricant is most stressed.

Trailing edge or discharge side of the pad.
Oil leaving the load zone is hotter and more oxidized.

Oil grooves and edges.
Deposits can collect where flow changes direction or slows.

Bearing ends and drain areas.
Oil can linger, cool, and drop out varnish precursors.

Journal witness band.
This is the polished rotating surface where transferred varnish, wiping, or thermal staining becomes visible.

Your photos show broad amber/brown bands on the journal, which suggests the deposit is not random rust. It follows the bearing contact/oil-film zone.

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6. Varnish vs heat tint vs rust: how to tell

The photos look consistent with oil varnish, but a photo alone cannot prove it. Use these checks:

Observation	More likely varnish	More likely heat tint / metal oxidation	More likely rust
Amber, honey, brown, glossy film	Yes	Sometimes	No
Wipes partly with solvent/clean cloth	Yes	No	Sometimes
Surface underneath remains smooth	Yes	Sometimes	No
Blue/purple/straw color in metal after cleaning	No	Yes	No
Rough pitting	No	Possible if severe	Yes
Sticky residue on bearing pads or oil grooves	Yes	No	Sometimes mixed
Matching pad deposit	Strong evidence	Possible rubbing evidence	No

Important distinction:

If the brown color can be removed chemically or by gentle wiping, it is probably varnish/deposit.
If the color remains in the metal after cleaning, it may be thermal discoloration from overheating.

The third image appears to show a broad amber glazed band, which is more typical of varnish/deposit. If there is also blue/purple metal color underneath, then overheating or wiping may also be involved.

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7. Why varnish forms in this area

Common causes include:

High oil temperature or local hot spots.
Heat accelerates oxidation and can make varnish precursors plate out. Pall lists high operating temperature and hot spots as varnish indicators and notes that higher temperature accelerates oil oxidation. (Pall)

Restricted oil flow.
Low flow reduces cooling and increases residence time.

Oil oxidation.
Air, heat, moisture, and time degrade oil. WearCheck identifies heat, air, moisture, additive depletion, contamination, and wear metals such as iron and copper as contributors to varnish formation.

Additive depletion.
Antioxidants and dispersants become consumed. Once the oil cannot hold degradation products in solution, deposits form.

Contamination.
Water, dirt, process chemicals, cleaning chemicals, mixed incompatible oils, and wear metals can accelerate varnish.

High shear in the bearing film.
The oil film in a journal bearing is thin and heavily sheared. Local thermal stress can be much higher than the bulk oil temperature suggests.

Start-stop operation.
During start-up and shutdown, the oil film may be incomplete, allowing mixed lubrication and wiping of deposits.

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8. Which side should be inspected first?

For the condition shown in your photos, inspect in this order:

1. Bearing pads/shells, especially the loaded area.
Look for amber/brown glaze, wiping, embedded particles, dull patches, edge loading, or babbitt distress.

2. Oil grooves and feed holes.
Check for sticky deposits, blocked passages, or uneven feed.

3. Bearing drain and end areas.
These often reveal varnish accumulation.

4. Journal surface.
Check whether the stain is removable, whether there is scoring, whether the shaft is out-of-round, and whether the surface finish has changed.

5. Oil system.
Check filters, cooler, tank, return lines, and servo/control components if present.

The journal mark is important, but the bearing pad condition will tell you more about the root cause.

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9. What operating symptoms usually accompany bearing varnish

Varnish in journal bearings can cause:

Increased bearing metal temperature.
Temperature cycling or sawtooth temperature behavior.
Higher vibration.
Rotor position shift.
Reduced oil clearance.
Poor heat transfer from bearing to oil.
Filter plugging or sticky deposits elsewhere in the oil system.

STLE notes that varnish on journal bearing pads can lead to elevated bearing temperature and vibration, and that bearings affected by varnish can show temperature increases as deposits build. (stle.org)

A key warning sign is this pattern:

Temperature slowly rises → machine is opened/cleaned → temperature drops → varnish builds again → temperature rises again.

That points strongly toward varnish, not only mechanical misalignment.

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10. Recommended tests

Do not rely only on visual inspection. Suggested oil and component checks:

Oil analysis

MPC / membrane patch colorimetry for varnish potential.
Acid number.
FTIR oxidation/nitration.
RULER antioxidant remaining life.
Water content.
Particle count.
Viscosity.
Ferrous and non-ferrous wear metals.
RPVOT or oxidation stability where applicable.

WearCheck notes that acid number alone cannot predict varnish-forming tendency, and describes MPC as a varnish-potential tool with action levels.

Bearing inspection

Pad temperature history.
Pad wiping pattern.
Babbitt condition.
Oil groove cleanliness.
Clearance measurement.
Contact pattern.
Journal runout and surface finish.
Shaft hardness or heat tint check if overheating is suspected.

System inspection

Oil cooler performance.
Oil flow rate and pressure.
Filter condition.
Reservoir temperature.
Foaming/aeration.
Water ingress.
Wrong oil top-up or oil mixing history.

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11. What not to conclude too quickly

Do not immediately conclude:

“The journal caused the varnish.”
The journal only shows the evidence.

Do not immediately conclude:

“The bearing material failed.”
The bearing may be a victim of oil degradation and thermal stress.

Do not immediately conclude:

“Changing the oil will fix it.”
Deposited varnish already inside the machine can re-contaminate fresh oil. WearCheck specifically warns that oil remaining in the system and varnish on interior surfaces can “poison” new oil, causing rapid degradation again.

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12. Corrective action strategy

A good correction plan is:

Step 1: Confirm the deposit.
Try a controlled wipe/solvent check on a small area. Confirm whether it is removable deposit or true heat tint.

Step 2: Inspect bearing pads.
The bearing pads/shells are the most important evidence.

Step 3: Check oil varnish potential.
Run MPC and antioxidant testing, not only standard oil analysis.

Step 4: Restore oil flow and cooling.
Verify oil pressure, flow, cooler approach temperature, feed restriction, drain restriction, and aeration.

Step 5: Remove varnish from the system.
Use proper varnish removal or flushing methods. Standard particle filters may not remove soluble varnish precursors effectively. STLE notes that mechanical filtration removes solids but does not address the chemistry of soluble varnish precursors. (stle.org)

Step 6: Clean/replace affected bearing parts as needed.
Do not polish away bearing geometry. If the babbitt/pad surface is wiped, cracked, embedded with debris, or clearance is reduced, replacement or rework may be needed.

Step 7: Recheck after restart.
Track bearing temperature, vibration, oil pressure, and MPC trend. A stable low temperature after cleaning but rising trend later suggests varnish is still forming.

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13. Practical conclusion for your photos

The brown/golden staining is on the journal, but the likely varnish formation problem belongs to the journal bearing lubrication system.

The most likely sequence is:

Oil degradation starts in the lubricant → varnish precursors circulate → deposits first stabilize on stationary bearing surfaces, grooves, edges, and hot/low-flow zones → clearance and heat transfer are affected → journal receives amber/brown witness staining.

So, to your question:

Journal or bearing?
Visible mark: journal.
Root problem: bearing/oil-system varnish condition.

Where does varnishing happen first?
Chemically: in the oil.
Mechanically inside the bearing: usually on the stationary bearing pads/shells and oil-flow areas before the journal.
Visually during inspection: often the journal shows it clearly as a brown witness band.