diff --git a/src/operators/arrange/upsert.rs b/src/operators/arrange/upsert.rs
index 8e0ee89a3..cfabfd472 100644
--- a/src/operators/arrange/upsert.rs
+++ b/src/operators/arrange/upsert.rs
@@ -109,7 +109,7 @@ use timely::progress::Antichain;
 use timely::dataflow::operators::Capability;
 
 use crate::operators::arrange::arrangement::Arranged;
-use crate::trace::Builder;
+use crate::trace::{Builder, Description};
 use crate::trace::{self, Trace, TraceReader, Batch, Cursor};
 use crate::trace::cursor::IntoOwned;
 use crate::{ExchangeData, Hashable};
@@ -281,7 +281,8 @@ where
                                     updates.sort();
                                     builder.push(&mut updates);
                                 }
-                                let batch = builder.done(prev_frontier.clone(), upper.clone(), Antichain::from_elem(G::Timestamp::minimum()));
+                                let description = Description::new(prev_frontier.clone(), upper.clone(), Antichain::from_elem(G::Timestamp::minimum()));
+                                let batch = builder.done(description);
                                 prev_frontier.clone_from(&upper);
 
                                 // Communicate `batch` to the arrangement and the stream.
diff --git a/src/operators/reduce.rs b/src/operators/reduce.rs
index 0b014c645..886c13d67 100644
--- a/src/operators/reduce.rs
+++ b/src/operators/reduce.rs
@@ -23,7 +23,7 @@ use crate::trace::cursor::IntoOwned;
 
 use crate::operators::arrange::{Arranged, ArrangeByKey, ArrangeBySelf, TraceAgent};
 use crate::lattice::Lattice;
-use crate::trace::{Batch, BatchReader, Cursor, Trace, Builder, ExertionLogic};
+use crate::trace::{Batch, BatchReader, Cursor, Trace, Builder, ExertionLogic, Description};
 use crate::trace::cursor::CursorList;
 use crate::trace::implementations::{KeySpine, KeyBuilder, ValSpine, ValBuilder};
 
@@ -565,7 +565,8 @@ where
 
                             if output_upper.borrow() != output_lower.borrow() {
 
-                                let batch = builder.done(output_lower.clone(), output_upper.clone(), Antichain::from_elem(G::Timestamp::minimum()));
+                                let description = Description::new(output_lower.clone(), output_upper.clone(), Antichain::from_elem(G::Timestamp::minimum()));
+                                let batch = builder.done(description);
 
                                 // ship batch to the output, and commit to the output trace.
                                 output.session(&capabilities[index]).give(batch.clone());
diff --git a/src/trace/implementations/merge_batcher.rs b/src/trace/implementations/merge_batcher.rs
index 63d724979..90e13508e 100644
--- a/src/trace/implementations/merge_batcher.rs
+++ b/src/trace/implementations/merge_batcher.rs
@@ -12,7 +12,7 @@ use timely::container::{ContainerBuilder, PushInto};
 
 use crate::difference::Semigroup;
 use crate::logging::{BatcherEvent, DifferentialEvent};
-use crate::trace::{Batcher, Builder};
+use crate::trace::{Batcher, Builder, Description};
 use crate::Data;
 
 /// Creates batches from unordered tuples.
@@ -109,7 +109,8 @@ where
 
         self.stash.clear();
 
-        let seal = B::seal(&mut readied, self.lower.borrow(), upper.borrow(), Antichain::from_elem(M::Time::minimum()).borrow());
+        let description = Description::new(self.lower.clone(), upper.clone(), Antichain::from_elem(M::Time::minimum()));
+        let seal = B::seal(&mut readied, description);
         self.lower = upper;
         seal
     }
diff --git a/src/trace/implementations/ord_neu.rs b/src/trace/implementations/ord_neu.rs
index 26270c004..f0c18a3c4 100644
--- a/src/trace/implementations/ord_neu.rs
+++ b/src/trace/implementations/ord_neu.rs
@@ -682,7 +682,7 @@ mod val_batch {
         }
 
         #[inline(never)]
-        fn done(mut self, lower: Antichain<Self::Time>, upper: Antichain<Self::Time>, since: Antichain<Self::Time>) -> OrdValBatch<L> {
+        fn done(mut self, description: Description<Self::Time>) -> OrdValBatch<L> {
             // Record the final offsets
             self.result.vals_offs.push(self.result.times.len());
             // Remove any pending singleton, and if it was set increment our count.
@@ -691,23 +691,18 @@ mod val_batch {
             OrdValBatch {
                 updates: self.result.times.len() + self.singletons,
                 storage: self.result,
-                description: Description::new(lower, upper, since),
+                description,
             }
         }
 
-        fn seal(
-            chain: &mut Vec<Self::Input>,
-            lower: AntichainRef<Self::Time>,
-            upper: AntichainRef<Self::Time>,
-            since: AntichainRef<Self::Time>,
-        ) -> Self::Output {
+        fn seal(chain: &mut Vec<Self::Input>, description: Description<Self::Time>) -> Self::Output {
             let (keys, vals, upds) = Self::Input::key_val_upd_counts(&chain[..]);
             let mut builder = Self::with_capacity(keys, vals, upds);
             for mut chunk in chain.drain(..) {
                 builder.push(&mut chunk);
             }
     
-            builder.done(lower.to_owned(), upper.to_owned(), since.to_owned())
+            builder.done(description)
         }
     }
 }
@@ -1170,7 +1165,7 @@ mod key_batch {
         }
 
         #[inline(never)]
-        fn done(mut self, lower: Antichain<Self::Time>, upper: Antichain<Self::Time>, since: Antichain<Self::Time>) -> OrdKeyBatch<L> {
+        fn done(mut self, description: Description<Self::Time>) -> OrdKeyBatch<L> {
             // Record the final offsets
             self.result.keys_offs.push(self.result.times.len());
             // Remove any pending singleton, and if it was set increment our count.
@@ -1178,23 +1173,18 @@ mod key_batch {
             OrdKeyBatch {
                 updates: self.result.times.len() + self.singletons,
                 storage: self.result,
-                description: Description::new(lower, upper, since),
+                description,
             }
         }
 
-        fn seal(
-            chain: &mut Vec<Self::Input>,
-            lower: AntichainRef<Self::Time>,
-            upper: AntichainRef<Self::Time>,
-            since: AntichainRef<Self::Time>,
-        ) -> Self::Output {
+        fn seal(chain: &mut Vec<Self::Input>, description: Description<Self::Time>) -> Self::Output {
             let (keys, vals, upds) = Self::Input::key_val_upd_counts(&chain[..]);
             let mut builder = Self::with_capacity(keys, vals, upds);
             for mut chunk in chain.drain(..) {
                 builder.push(&mut chunk);
             }
     
-            builder.done(lower.to_owned(), upper.to_owned(), since.to_owned())
+            builder.done(description)
         }
     }
 
diff --git a/src/trace/implementations/rhh.rs b/src/trace/implementations/rhh.rs
index 5a57d37a5..4c1ac9a11 100644
--- a/src/trace/implementations/rhh.rs
+++ b/src/trace/implementations/rhh.rs
@@ -855,7 +855,7 @@ mod val_batch {
         }
 
         #[inline(never)]
-        fn done(mut self, lower: Antichain<Self::Time>, upper: Antichain<Self::Time>, since: Antichain<Self::Time>) -> RhhValBatch<L> {
+        fn done(mut self, description: Description<Self::Time>) -> RhhValBatch<L> {
             // Record the final offsets
             self.result.vals_offs.push(self.result.times.len());
             // Remove any pending singleton, and if it was set increment our count.
@@ -864,23 +864,18 @@ mod val_batch {
             RhhValBatch {
                 updates: self.result.times.len() + self.singletons,
                 storage: self.result,
-                description: Description::new(lower, upper, since),
+                description,
             }
         }
 
-        fn seal(
-            chain: &mut Vec<Self::Input>,
-            lower: AntichainRef<Self::Time>,
-            upper: AntichainRef<Self::Time>,
-            since: AntichainRef<Self::Time>,
-        ) -> Self::Output {
+        fn seal(chain: &mut Vec<Self::Input>, description: Description<Self::Time>) -> Self::Output {
             let (keys, vals, upds) = Self::Input::key_val_upd_counts(&chain[..]);
             let mut builder = Self::with_capacity(keys, vals, upds);
             for mut chunk in chain.drain(..) {
                 builder.push(&mut chunk);
             }
-    
-            builder.done(lower.to_owned(), upper.to_owned(), since.to_owned())
+
+            builder.done(description)
         }
     }
 
diff --git a/src/trace/mod.rs b/src/trace/mod.rs
index 4a85747c2..7ea9064fa 100644
--- a/src/trace/mod.rs
+++ b/src/trace/mod.rs
@@ -342,18 +342,14 @@ pub trait Builder: Sized {
     /// Adds all elements from `chunk` to the builder and leaves `chunk` in an undefined state.
     fn push(&mut self, chunk: &mut Self::Input);
     /// Completes building and returns the batch.
-    fn done(self, lower: Antichain<Self::Time>, upper: Antichain<Self::Time>, since: Antichain<Self::Time>) -> Self::Output;
+    fn done(self, description: Description<Self::Time>) -> Self::Output;
 
     /// Builds a batch from a chain of updates corresponding to the indicated lower and upper bounds.
     ///
     /// This method relies on the chain only containing updates greater or equal to the lower frontier,
-    /// and not greater or equal to the upper frontier. Chains must also be sorted and consolidated.
-    fn seal(
-        chain: &mut Vec<Self::Input>,
-        lower: AntichainRef<Self::Time>,
-        upper: AntichainRef<Self::Time>,
-        since: AntichainRef<Self::Time>,
-    ) -> Self::Output;
+    /// and not greater or equal to the upper frontier, as encoded in the description. Chains must also
+    /// be sorted and consolidated.
+    fn seal(chain: &mut Vec<Self::Input>, description: Description<Self::Time>) -> Self::Output;
 }
 
 /// Represents a merge in progress.
@@ -467,14 +463,9 @@ pub mod rc_blanket_impls {
         type Output = Rc<B::Output>;
         fn with_capacity(keys: usize, vals: usize, upds: usize) -> Self { RcBuilder { builder: B::with_capacity(keys, vals, upds) } }
         fn push(&mut self, input: &mut Self::Input) { self.builder.push(input) }
-        fn done(self, lower: Antichain<Self::Time>, upper: Antichain<Self::Time>, since: Antichain<Self::Time>) -> Rc<B::Output> { Rc::new(self.builder.done(lower, upper, since)) }
-        fn seal(
-            chain: &mut Vec<Self::Input>,
-            lower: AntichainRef<Self::Time>,
-            upper: AntichainRef<Self::Time>,
-            since: AntichainRef<Self::Time>,
-        ) -> Self::Output {
-            Rc::new(B::seal(chain, lower, upper, since))
+        fn done(self, description: Description<Self::Time>) -> Rc<B::Output> { Rc::new(self.builder.done(description)) }
+        fn seal(chain: &mut Vec<Self::Input>, description: Description<Self::Time>) -> Self::Output {
+            Rc::new(B::seal(chain, description))
         }
     }