diff --git a/src/legendhpges/base.py b/src/legendhpges/base.py
index d37b4a9..bb7d332 100644
--- a/src/legendhpges/base.py
+++ b/src/legendhpges/base.py
@@ -9,7 +9,7 @@
 from pint import Quantity
 from pyg4ometry import geant4
 
-from .materials import natural_germanium
+from .materials import make_natural_germanium
 from .registry import default_g4_registry
 from .registry import default_units_registry as u
 
@@ -36,7 +36,7 @@ def __init__(
         metadata: str | dict | AttrsDict,
         name: str | None = None,
         registry: geant4.Registry = default_g4_registry,
-        material: geant4.MaterialCompound = natural_germanium,
+        material: geant4.MaterialCompound = None,
     ) -> None:
         if registry is None:
             msg = "registry cannot be None"
@@ -46,6 +46,9 @@ def __init__(
             msg = "metadata cannot be None"
             raise ValueError(msg)
 
+        if material is None:
+            material = make_natural_germanium(registry)
+
         # build crystal, declare as detector
         if not isinstance(metadata, (dict, AttrsDict)):
             with Path(metadata).open() as jfile:
diff --git a/src/legendhpges/make_hpge.py b/src/legendhpges/make_hpge.py
index 35c38bb..2b69921 100644
--- a/src/legendhpges/make_hpge.py
+++ b/src/legendhpges/make_hpge.py
@@ -71,7 +71,7 @@ def make_hpge(
             enrichment = gedet_meta.production.enrichment
         else:
             enrichment = gedet_meta.production.enrichment.val
-        kwargs["material"] = make_enriched_germanium(enrichment)
+        kwargs["material"] = make_enriched_germanium(enrichment, registry)
 
     if name is None:
         if gedet_meta.name is None:
diff --git a/src/legendhpges/materials.py b/src/legendhpges/materials.py
index 65b348b..84023a3 100644
--- a/src/legendhpges/materials.py
+++ b/src/legendhpges/materials.py
@@ -56,23 +56,22 @@ def _number_density_meas() -> Quantity:
     return n_avogadro * natge_density_meas / a_eff
 
 
-def _make_natural_germanium() -> g4.MaterialCompound:
+def make_natural_germanium(
+    registry: g4.Registry = default_g4_registry,
+) -> g4.MaterialCompound:
     """Natural germanium material builder."""
     enrge_name = "NaturalGermanium"
 
-    if enrge_name not in default_g4_registry.materialDict:
+    if enrge_name not in registry.materialDict:
         enrge = g4.ElementIsotopeMixture(enrge_name, "NatGe", len(natge_isotopes))
 
         for iso, frac in natge_isotopes.items():
             enrge.add_isotope(iso, frac)
 
-        matenrge = g4.MaterialCompound(
-            enrge_name, natge_density_meas.m, 1, default_g4_registry
-        )
+        matenrge = g4.MaterialCompound(enrge_name, natge_density_meas.m, 1, registry)
         matenrge.add_element_massfraction(enrge, 1)
-    else:
-        matenrge = default_g4_registry.materialDict[enrge_name]
-    return matenrge
+
+    return registry.materialDict[enrge_name]
 
 
 def enriched_germanium_density(ge76_fraction: float = 0.92) -> Quantity:
@@ -90,7 +89,10 @@ def enriched_germanium_density(ge76_fraction: float = 0.92) -> Quantity:
     return (_number_density_meas() * m_eff / n_avogadro).to("g/cm^3")
 
 
-def make_enriched_germanium(ge76_fraction: float = 0.92) -> g4.Material:
+def make_enriched_germanium(
+    ge76_fraction: float = 0.92,
+    registry: g4.Registry = default_g4_registry,
+) -> g4.Material:
     """Enriched germanium material builder.
 
     Note
@@ -104,8 +106,8 @@ def make_enriched_germanium(ge76_fraction: float = 0.92) -> g4.Material:
     """
     enrge_name = f"EnrichedGermanium{ge76_fraction:.3f}"
 
-    if enrge_name not in default_g4_registry.materialDict:
-        enrge = g4.ElementIsotopeMixture(enrge_name, "EnrGe", 2)
+    if enrge_name not in registry.materialDict:
+        enrge = g4.ElementIsotopeMixture(f"Element{enrge_name}", "EnrGe", 2, registry)
         enrge.add_isotope(ge74, 1 - ge76_fraction)
         enrge.add_isotope(ge76, ge76_fraction)
 
@@ -113,13 +115,8 @@ def make_enriched_germanium(ge76_fraction: float = 0.92) -> g4.Material:
             enrge_name,
             enriched_germanium_density(ge76_fraction).to("g/cm^3").m,
             1,
-            default_g4_registry,
+            registry,
         )
         matenrge.add_element_massfraction(enrge, 1)
-    else:
-        matenrge = default_g4_registry.materialDict[enrge_name]
-    return matenrge
-
 
-natural_germanium: g4.MaterialCompound = _make_natural_germanium()
-enriched_germanium: g4.MaterialCompound = make_enriched_germanium()
+    return registry.materialDict[enrge_name]
diff --git a/tests/test_det_profile.py b/tests/test_det_profile.py
index 7849097..12ab996 100644
--- a/tests/test_det_profile.py
+++ b/tests/test_det_profile.py
@@ -18,9 +18,10 @@
     SemiCoax,
     make_hpge,
 )
-from legendhpges.materials import natural_germanium
+from legendhpges.materials import make_natural_germanium
 
 reg = geant4.Registry()
+natural_germanium = make_natural_germanium(reg)
 configs = TextDB(pathlib.Path(__file__).parent.resolve() / "configs")
 
 
diff --git a/tests/test_materials.py b/tests/test_materials.py
index 91eae7f..93010cc 100644
--- a/tests/test_materials.py
+++ b/tests/test_materials.py
@@ -26,6 +26,6 @@ def test_g4_materials():
         == materials.enriched_germanium_density(0.92).to("g/cm^3").m
     )
     assert (
-        materials.natural_germanium.density
+        materials.make_natural_germanium().density
         == materials.natge_density_meas.to("g/cm^3").m
     )