diff --git a/src/material.cc b/src/material.cc
index 113c26d25b..a995fd5aec 100644
--- a/src/material.cc
+++ b/src/material.cc
@@ -104,10 +104,17 @@ Material::Ptr Material::ExtractComp(double qty, Composition::Ptr c,
 
 void Material::Absorb(Material::Ptr mat) {
 
-  // force both mateiral objects to advance to the same decay time
-  int common_decay_time = std::max(this->prev_decay_time_, mat->prev_decay_time_);
-  if (ctx_ != NULL && ctx_->sim_info().decay != "never") {
+  // Handle absorb-specific decay rules
+  int common_decay_time;
+  if (HasContext() && mat->HasContext()) {
     common_decay_time = ctx_->time();    
+  } else if (!HasContext() && !mat->HasContext() 
+              && mat->prev_decay_time_ > prev_decay_time_) {
+    throw ValueError("Cannot absorb a material that is more decayed than this one");
+  } else if (HasContext() != mat->HasContext()) {
+    throw cyclus::Error("Cannot combine a tracked and untracked material!");
+  } else {
+    common_decay_time = prev_decay_time_;
   }
   mat->Decay(common_decay_time);
   this->Decay(common_decay_time);
@@ -128,7 +135,12 @@ void Material::Absorb(Material::Ptr mat) {
     comp_ = Composition::CreateFromMass(compmath::Add(v, otherv));
   }
   
-  qty_ += mat->qty_;
+  double tot_mass = qty_ + mat->quantity();
+  double avg_unit_value =
+      (qty_ * UnitValue() + mat->quantity() * mat->UnitValue()) / tot_mass;
+  SetUnitValue(avg_unit_value);
+  qty_ = tot_mass;
+
   mat->qty_ = 0;
   tracker_.Absorb(&mat->tracker_);
 }
@@ -204,9 +216,14 @@ void Material::Decay(int curr_time) {
     curr_time = ctx_->time();
   }
 
+
   int dt = curr_time - prev_decay_time_;
-  if (dt == 0) {
-    return;
+  
+  // Block decay backwards and past sim time for materials in a context
+  if (ctx_ && (dt < 0 || curr_time > ctx_->time())) {
+    std::string msg = "Materials in a context cannot decay backwards or "
+                      "past the current simulation time!";
+    throw cyclus::Error(msg);
   }
 
   // eps_decay defined such that tritium (12.32 yr half life) decays over 1 day
@@ -243,7 +260,9 @@ void Material::Decay(int curr_time) {
     }
   }
 
-  prev_decay_time_ = curr_time;  // this must go before Transmute call
+  // Need to set prev_decay_time before Transmute.
+  prev_decay_time_ = curr_time; 
+  
   Composition::Ptr decayed = comp_->Decay(dt, secs_per_timestep);
   Transmute(decayed);
 }
diff --git a/src/material.h b/src/material.h
index 9ed29950b4..2e7635069a 100644
--- a/src/material.h
+++ b/src/material.h
@@ -108,6 +108,9 @@ class Material : public Resource {
   /// Returns the mass of this material in kg.
   virtual double quantity() const;
 
+  /// Returns true if the material has a context, false otherwise.
+  virtual bool HasContext() const {return ctx_ != NULL;}
+
   virtual Resource::Ptr ExtractRes(double qty);
 
   /// Same as ExtractComp with c = this->comp().
diff --git a/tests/material_tests.cc b/tests/material_tests.cc
index a75cc22ee2..48442fa58b 100644
--- a/tests/material_tests.cc
+++ b/tests/material_tests.cc
@@ -134,6 +134,42 @@ TEST_F(MaterialTest, AbsorbIntoZeroMaterial) {
   EXPECT_FLOAT_EQ(test_size_, same_as_test_mat->quantity());
 }
 
+TEST_F(MaterialTest, AbsorbMatlWithoutContext) {
+  Material::Ptr no_ctx_mat = Material::CreateUntracked(0, test_comp_);
+  EXPECT_FALSE(no_ctx_mat->HasContext());
+
+  // Since test_mat_ and no_ctx_mat both don't have context this is fine
+  EXPECT_NO_THROW(test_mat_->Absorb(no_ctx_mat));
+}
+
+TEST_F(MaterialTest, DecayTiming) {
+  FakeContext* fake_ctx = new FakeContext(&ti, &rec);
+  TestFacility* fake_fac = new TestFacility(fake_ctx);
+
+  double untracked_qty = 1.0;
+
+  Material::Ptr m1 = Material::Create(fake_fac, 1, diff_comp_);
+  Material::Ptr m2 = Material::CreateUntracked(untracked_qty, diff_comp_);
+
+  // Set context time to 10 to match the decay time
+  fake_ctx->time(10);
+
+  m1->Decay(); // decay m1 to time 10
+  EXPECT_EQ(10, m1->prev_decay_time());
+  EXPECT_ANY_THROW(m1->Decay(9)); // no backwards decay for tracked mats
+  EXPECT_ANY_THROW(m1->Decay(1000)); // tracked can't decay past sim time
+
+  m2->Decay(10); // decay m2 to time 10
+  EXPECT_EQ(10, m2->prev_decay_time());
+  EXPECT_NO_THROW(m2->Decay(6)); // Backwards decay is fine if untracked
+  EXPECT_EQ(6, m2->prev_decay_time()); // correctly updates prev_decay_time_
+  EXPECT_NO_THROW(m2->Decay(1000)); // Arbitrary decay fine on untracked
+  EXPECT_EQ(1000, m2->prev_decay_time());
+
+  delete fake_fac;
+  delete fake_ctx;
+}
+
 TEST_F(MaterialTest, ExtractMass) {
   double amt = test_size_ / 3;
   double diff = test_size_ - amt;
@@ -211,15 +247,15 @@ TEST_F(MaterialTest, ExtractInGrams) {
 
 TEST_F(MaterialTest, DecayResBuf) {
   // prequeries
-  cyclus::toolkit::MatQuery orig(tracked_mat_);
+  cyclus::toolkit::MatQuery orig(untracked_mat_);
   double u235_qty = orig.mass(u235_);
   double pb208_qty = orig.mass(pb208_);
   double am241_qty = orig.mass(am241_);
   double sr89_qty = orig.mass(sr89_);
-  double orig_mass = tracked_mat_->quantity();
+  double orig_mass = untracked_mat_->quantity();
 
   cyclus::toolkit::ResBuf<cyclus::Material> res_buf;
-  res_buf.Push(tracked_mat_);
+  res_buf.Push(untracked_mat_); // use untracked mat so we can forward decay
   // decay for 2 months which is just over 1 Sr-89 half-life
   res_buf.Decay(2);
   cyclus::Material::Ptr pop_mat = res_buf.Pop();
@@ -236,17 +272,17 @@ TEST_F(MaterialTest, DecayResBuf) {
 
 TEST_F(MaterialTest, DecayManual) {
   // prequeries
-  cyclus::toolkit::MatQuery orig(tracked_mat_);
+  cyclus::toolkit::MatQuery orig(untracked_mat_);
   double u235_qty = orig.mass(u235_);
   double pb208_qty = orig.mass(pb208_);
   double am241_qty = orig.mass(am241_);
   double sr89_qty = orig.mass(sr89_);
-  double orig_mass = tracked_mat_->quantity();
+  double orig_mass = untracked_mat_->quantity();
 
-  tracked_mat_->Decay(100);
+  untracked_mat_->Decay(100);
 
   // postquery
-  cyclus::toolkit::MatQuery mq(tracked_mat_);
+  cyclus::toolkit::MatQuery mq(untracked_mat_);
 
   // postchecks
   EXPECT_NE(u235_qty, mq.mass(u235_));
@@ -353,20 +389,22 @@ TEST_F(MaterialTest, DecayCustomTimeStep) {
   cyclus::Env::SetNucDataPath();
   std::string cs137 ("Cs137");
   uint64_t custom_timestep = pyne::half_life(cs137);
+  double qty = 1.0;
 
   SimInfo si(10, 2015, 1, "", "manual");
   si.dt = custom_timestep;
-  cyclus::Context ctx(&ti, &rec);
-  ctx.InitSim(si);
-  Agent* a = new TestFacility(&ctx);
+  FakeContext* fake_ctx = new FakeContext(&ti, &rec);
+  fake_ctx->InitSim(si);
 
   CompMap v;
   v[id("Cs137")] = 1;
   Composition::Ptr c = Composition::CreateFromAtom(v);
   CompMap tmp = c->atom();
-  Material::Ptr m = Material::Create(a, 1.0, c);
+  TestFacility* fake_fac = new TestFacility(fake_ctx);
+  Material::Ptr m = Material::Create(fake_fac, qty, c);
 
-  m->Decay(1);
+  fake_ctx->time(1);
+  m->Decay();
 
   Composition::Ptr newc = m->comp();
   CompMap newv = newc->atom();
@@ -375,14 +413,17 @@ TEST_F(MaterialTest, DecayCustomTimeStep) {
   // one half of atoms should have decayed away
   double eps = cyclus::CY_NEAR_ZERO;
   EXPECT_NEAR(0.5, newv[id("Cs137")], eps) << "one Cs137 half-life duration time step did not decay half of Cs atoms";
+
+  delete fake_fac;
+  delete fake_ctx;
 }
 
 TEST_F(MaterialTest, ExtractPrevDecay) {
-  tracked_mat_->Decay(10);
-  double qty = tracked_mat_->quantity() / 2;
-  cyclus::Material::Ptr x = tracked_mat_->ExtractQty(qty);
+  untracked_mat_->Decay(10);
+  double qty = untracked_mat_->quantity() / 2;
+  cyclus::Material::Ptr x = untracked_mat_->ExtractQty(qty);
 
-  EXPECT_EQ(tracked_mat_->prev_decay_time(), x->prev_decay_time());
+  EXPECT_EQ(untracked_mat_->prev_decay_time(), x->prev_decay_time());
 }
 
 // Transmute should reset a material's prev_decay_time to the current
@@ -408,23 +449,48 @@ TEST_F(MaterialTest, TransmutePrevDecay) {
 // as coded.  We may decide to change the behavior in the future breaking
 // this test; the test will need to be modified accordingly.
 //
-// This test checks to see that, when materials are absorbed together, the
-// previous decay time for the larger quantity material is used as the value
-// for the new, combined material.
+// This test checks to see that, when materials are absorbed together, both 
+// materials are decayed prior to the absorption.
+
 TEST_F(MaterialTest, AbsorbPrevDecay) {
-  Material::Ptr m1 = Material::Create(fac, 1, diff_comp_);
-  Material::Ptr m2 = Material::Create(fac, 1, diff_comp_);
-  Material::Ptr m3 = Material::Create(fac, 1000, diff_comp_);
-  m3->Decay(10);
+  FakeContext* fake_ctx = new FakeContext(&ti, &rec);
+  TestFacility* fake_fac = new TestFacility(fake_ctx);
+
+  double untracked_qty = 1.0;
+
+  Material::Ptr m1 = Material::Create(fake_fac, 1, diff_comp_);
+  Material::Ptr m2 = Material::Create(fake_fac, 1, diff_comp_);
+  Material::Ptr m3 = Material::Create(fake_fac, 1000, diff_comp_);
+  Material::Ptr m4 = Material::CreateUntracked(untracked_qty, diff_comp_);
+  Material::Ptr m5 = Material::CreateUntracked(untracked_qty, diff_comp_);
+
+  // Set context time to 10 to match the decay time
+  fake_ctx->time(10);
 
+  m3->Decay(); // decay m3 to time 10
   EXPECT_EQ(0, m1->prev_decay_time());
   EXPECT_EQ(0, m2->prev_decay_time());
   EXPECT_EQ(10, m3->prev_decay_time());
 
+  fake_ctx->time(11);
+
   m1->Absorb(m3);
-  EXPECT_EQ(10, m1->prev_decay_time());
+  EXPECT_EQ(11, m1->prev_decay_time());
   m1->Absorb(m2);
-  EXPECT_EQ(10, m1->prev_decay_time());
+  EXPECT_EQ(11, m1->prev_decay_time());
+
+  // We shouldn't be able to absorb a more-decayed untracked material 
+  // but we should be able to absorb materials not in a context.
+  m4->Decay(11);
+  EXPECT_ANY_THROW(m5->Absorb(m4));
+  EXPECT_NO_THROW(m4->Absorb(m5));
+
+  // Can't combine a tracked an untracked mat
+  EXPECT_ANY_THROW(m1->Absorb(m5));
+  EXPECT_ANY_THROW(m5->Absorb(m1));
+
+  delete fake_fac;
+  delete fake_ctx;
 }
 
 TEST_F(MaterialTest, DecayHeatTest) {
@@ -449,14 +515,24 @@ TEST_F(MaterialTest, DecaySmallAmount) {
   v[tritium_id] = 1.0;
   Composition::Ptr tritium_comp = Composition::CreateFromMass(v);
 
+  // Set up the one day time step context
+  int one_day = 86400;
+  cyclus::Timer ti_day_timestep;
+  si_day_timestep = SimInfo(100, 2015, 1, "", "manual");
+  si_day_timestep.dt = one_day;
+  FakeContext* ctx_day_timestep = new FakeContext(&ti_day_timestep, &rec);
+  ctx_day_timestep->InitSim(si_day_timestep);
+  TestFacility* fac_day_timestep = new TestFacility(ctx_day_timestep);
+
   Material::Ptr tritium = Material::Create(fac_day_timestep, qty, tritium_comp);
 
   cyclus::toolkit::MatQuery mq(tritium);
   double start_qty = mq.mass(tritium_id);
   EXPECT_EQ(qty, start_qty);
 
-  // Decay forward by one day (we use the one day time step facility)
-  tritium->Decay(1);
+  // Decay forward by one day (we have to push the fake_ctx's time forward first)
+  ctx_day_timestep->time(1);
+  tritium->Decay();
   double decayed_qty = mq.mass(tritium_id);
 
   // NOTE: we've already tested that Decay is decaying the correct amt, so we
diff --git a/tests/material_tests.h b/tests/material_tests.h
index bad25aabfa..efa826f3a9 100644
--- a/tests/material_tests.h
+++ b/tests/material_tests.h
@@ -11,6 +11,7 @@
 #include "test_agents/test_facility.h"
 #include "recorder.h"
 #include "timer.h"
+#include "test_context.h"
 
 
 namespace cyclus {
@@ -26,20 +27,19 @@ class MaterialTest : public ::testing::Test {
   Material::Ptr diff_mat_;
   Material::Ptr default_mat_;
   Material::Ptr tracked_mat_;
+  Material::Ptr untracked_mat_;
   Material::Ptr tracked_mat_no_decay_;
   long int u235_halflife_;
   int th228_halflife_;
   double u235_g_per_mol_;
 
   cyclus::Timer ti;
-  cyclus::Timer ti_day_timestep;
   cyclus::Recorder rec;
   cyclus::Context* ctx;
   TestFacility* fac;
   cyclus::Context* ctx_no_decay;
   TestFacility* fac_no_decay;
-  cyclus::Context* ctx_day_timestep;
-  TestFacility* fac_day_timestep;
+
   // dur 100, y0 = 2015, m0=1, handle="", d="never"
   SimInfo si;
   SimInfo si_day_timestep;
@@ -49,14 +49,6 @@ class MaterialTest : public ::testing::Test {
     ctx = new cyclus::Context(&ti, &rec);
     fac = new TestFacility(ctx);
 
-    // Set up the one day time step context
-    int one_day = 86400;
-    si_day_timestep = SimInfo(100, 2015, 1, "", "manual");
-    si_day_timestep.dt = one_day;
-    ctx_day_timestep = new cyclus::Context(&ti_day_timestep, &rec);
-    ctx_day_timestep->InitSim(si_day_timestep);
-    fac_day_timestep = new TestFacility(ctx_day_timestep);
-
     si = SimInfo(100, 2015, 1, "", "never");
     ctx_no_decay = new cyclus::Context(&ti, &rec);
     ctx_no_decay->InitSim(si);
@@ -88,6 +80,7 @@ class MaterialTest : public ::testing::Test {
     two_test_mat_ = Material::CreateUntracked(2 * test_size_, test_comp_);
     ten_test_mat_ = Material::CreateUntracked(10 * test_size_, test_comp_);
     diff_mat_ = Material::CreateUntracked(test_size_, diff_comp_);
+    untracked_mat_ = Material::CreateUntracked(1000, diff_comp_);
 
     // tracked material
     tracked_mat_ = Material::Create(fac, 1000, diff_comp_);