diff --git a/bambu_run/mcp/filaments.py b/bambu_run/mcp/filaments.py
index 9900ff4..4c916fe 100644
--- a/bambu_run/mcp/filaments.py
+++ b/bambu_run/mcp/filaments.py
@@ -80,3 +80,36 @@ def _spool_summary(f, include_history):
             for u in f.print_usages.select_related("print_job").order_by("-print_job__start_time")[:3]
         ]
     return entry
+
+
+def get_filament(filament_id: int) -> dict:
+    """One spool in full, plus its complete print-usage history.
+
+    Usage rows with corrupt consumption (negative, or derived from the -1
+    "unread" sentinel) are returned with consumed_grams null and
+    data_quality "unreliable" rather than dropped -- the print still
+    happened, and hiding it would misstate the spool's history. Raises
+    Filament.DoesNotExist if filament_id is unknown.
+    """
+    f = Filament.objects.get(id=filament_id)
+    summary = _spool_summary(f, include_history=False)
+
+    usages = []
+    for u in f.print_usages.select_related("print_job").order_by("-print_job__start_time"):
+        consumed_percent, consumed_grams, quality = normalize_consumed(
+            u.starting_percent, u.ending_percent, f.initial_weight_grams
+        )
+        usages.append({
+            "job_id": u.print_job_id,
+            "job_name": u.print_job.project_name,
+            "started_at": u.print_job.start_time.isoformat(),
+            "consumed_percent": consumed_percent,
+            "consumed_grams": consumed_grams,
+            "data_quality": quality,
+        })
+
+    return {
+        **summary,
+        "purchase_date": f.purchase_date.isoformat() if f.purchase_date else None,
+        "usage_history": usages,
+    }
diff --git a/tests/test_mcp_filaments.py b/tests/test_mcp_filaments.py
index c44d38d..a21b87d 100644
--- a/tests/test_mcp_filaments.py
+++ b/tests/test_mcp_filaments.py
@@ -2,7 +2,7 @@ import pytest
 from django.utils import timezone
 
 from bambu_run.models import Filament, Printer, PrintJob, FilamentUsage
-from bambu_run.mcp.filaments import list_filaments
+from bambu_run.mcp.filaments import list_filaments, get_filament
 
 
 @pytest.mark.django_db
@@ -97,3 +97,39 @@ def test_list_filaments_never_exposes_rfid_identifiers():
     entry_str = repr(result["filaments"][0])
     assert "SECRET-UUID" not in entry_str
     assert "SECRET-TAG" not in entry_str
+
+
+@pytest.mark.django_db
+def test_get_filament_returns_full_usage_history_with_data_quality():
+    p = Printer.objects.create(name="RNL-H2C", model="H2C", is_active=True)
+    f = Filament.objects.create(type="ABS", brand="Bambu Lab", color="Black", initial_weight_grams=1000)
+    job1 = PrintJob.objects.create(device=p, project_name="Bracket", start_time=timezone.now(), final_status="FINISH")
+    job2 = PrintJob.objects.create(device=p, project_name="Vase", start_time=timezone.now(), final_status="FINISH")
+    FilamentUsage.objects.create(print_job=job1, filament=f, tray_id=0, starting_percent=80, ending_percent=70)
+    FilamentUsage.objects.create(print_job=job2, filament=f, tray_id=0, starting_percent=-1, ending_percent=100)
+
+    result = get_filament(f.id)
+
+    assert len(result["usage_history"]) == 2
+    reliable = next(u for u in result["usage_history"] if u["job_name"] == "Bracket")
+    unreliable = next(u for u in result["usage_history"] if u["job_name"] == "Vase")
+    assert reliable["data_quality"] == "ok"
+    assert reliable["consumed_grams"] == 100
+    assert unreliable["data_quality"] == "unreliable"
+    assert unreliable["consumed_grams"] is None
+
+
+@pytest.mark.django_db
+def test_get_filament_never_exposes_purchase_price_or_cost():
+    f = Filament.objects.create(type="PLA", brand="Bambu Lab", color="White", purchase_price=25.50)
+
+    result = get_filament(f.id)
+
+    assert "purchase_price" not in result
+    assert "cost" not in result
+
+
+@pytest.mark.django_db
+def test_get_filament_unknown_id_raises():
+    with pytest.raises(Filament.DoesNotExist):
+        get_filament(999999)