In Jain tradition the sandalwood paste (chandan) on a Jina idol is not meant to be perfectly smooth or “paint‑like”. The uneven, patchy look actually comes from the way it is applied as a devotional act.

Here is the usual traditional process (it can vary slightly by sect and region):

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1. Preparation of the paste

• Pure sandalwood is rubbed on a stone with a little clean water (often filtered or boiled and cooled).
• The paste is kept in a clean container or on the same stone.
• The person preparing it should be in a state of śuddhi (cleanliness) – bathed, wearing clean clothes, with a peaceful mind, often reciting small sutras while preparing.

This already shows: the paste is not industrially smooth like commercial paint; it has a natural texture.

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2. Who applies it

• Generally applied by the pūjari or the devotee performing the snātra‑pūjā / abhiṣeka.
• They stand or sit near the idol, often after the abhiṣeka (water/milk, etc. bathing ritual).

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3. Basic points of application

Common pattern (especially in Śvetāmbara temples; Digambara temples sometimes do more minimal application):

1. Tilak on forehead

- A small round or vertical mark in the center of the forehead. - Made with the tip of the finger or thumb. - This is why you often see a thick, raised dot or oval – it is pressed, not brushed.

1. On the chest (ūrasa)

- Often two small circles or a small area in the center of the chest. - Applied with fingers, again giving a slightly uneven, finger‑shaped patch.

1. On the limbs (optional / according to local tradition)

- Some temples apply a bit on the shoulders, knees, or hands/feet. - Frequently done with small circular movements of the finger.

1. On the pedestal or around the feet

- Sometimes a thin smear or dots of sandalwood paste around the lotus, seat, or near the feet.

Because this is done with fingers in small dabs or circular motions, the layer is naturally uneven.

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4. Why it looks uneven (art-historical view)

From an art history perspective:

• Medium & tool:

- The “brush” is the human finger, not a flat brush. So you see: - finger‑tip circles - small patches with visible edges - varying thickness where the finger pressed harder or lighter

• Intention:

- The goal is puṇya and bhakti, not aesthetic smoothness. - The act is symbolic “cooling” and honoring the Jina, not “re-painting” the sculpture.

• Layering over time:

- After each pūjā, some residue remains even after gentle cleaning. Over months/years this can leave a slightly mottled or stained surface.

• Marble / stone interaction:

- On polished marble, the paste sometimes “slides” a bit when applied, making irregular borders. - On older or slightly porous stone, it adheres in tiny uneven grains.

So the “unevenness” is a result of ritual technique and devotional priority, not lack of skill.

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5. Sectarian / regional variations (very brief)

• Śvetāmbara:

- Often more visible use of chandan on forehead, chest, and sometimes more parts of the idol, especially during big pūjās and festivals.

• Digambara:

- In many temples the idol is kept relatively plain; sandalwood and other gandhas may be applied sparingly or mainly on certain parts (like forehead, chest) and often removed carefully. - Strong emphasis on preserving the original form and clarity of the idol.

Local traditions can add patterns (small lines, extra dots, etc.), but even then they are almost always done with fingers, keeping the slightly irregular look.

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6. If you want to study it as an art history student

You can observe and document:

• Finger‑mark patterns: shape, size, direction.
• Sequence: which parts get sandal first, and how many times.
• Texture: thickness, cracks when dried, color change over time.
• Impact on sculpture: how repeated application affects polish, patina, and visual reading of features (eyes, śrīvatsa, chest line, etc.).

This can give you a rich view of how ritual use slowly transforms the visual appearance of the idol, without changing its core iconography.

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If you wish, you can also specify a particular sect (Digambar/Śvetāmbara) or region, and I can outline the exact step‑by‑step pattern usually followed there.