Northern European Axe Head Replication Process

Step 1: Documentation

The axe head was documented through photogrammetry to create a 3D model. The photogrammetry process involved using a turntable and a camera in fixed positions to take pictures around and above the object at different angles and orientations. These photo sets were used to create a 3D model of the axe head using Agisoft Metashape.

Step 2: 3D Modeling and Printing

Once the 3D model was completed, it was used to 3D print a 1:1 replica of the artifact. The printing material was polylactic acid (PLA), which is a popular 3D printing material. The resulting print is rigid and can be used for many purposes, including making rubber molds. 

Our 3D Models:

(Coming Soon)

Step 3: Mold Making

The 3D-printed axe head was used to create a silicone rubber mold of the object. Smooth-On Silicone Mold Making Rubber Oomoo 30 and Smooth-On Universal Mold Release spray were used in the mold-making process.

Method 1:

The rubber was poured in two different iterations to result in a two-part silicone mold. The first side of the mold was poured on top of the PLA replica embedded in plasticine clay in a container. A small bolt was used to make impressions on the surface of the clay to act as “keys” for the mold, ensuring the two parts securely and accurately fit together. The object, clay, and container were all sprayed with mold release before pouring the rubber. After a six-hour curing time, the resulting half mold was taken out of the container. After removing the clay from the container, the half mold was placed back into the container object-side up and sprayed generously with mold release. Then, more rubber was poured into the container to complete the other side of the two-part mold.

During the removal of the axe head model, the silicone material ripped, rendering this mold unusable.

Method 2: 

The PLA replica was embedded into the bottom of a container made of plasticine clay. After spraying the clay and replica with mold release, the silicone rubber was poured into the container to submerge the object. This resulted in a one-part mold after a six-hour curing time. The 3D print was removed from the mold through the bottom of the clay container. Since the object was embedded in the clay, the mold did not encase the entire axe head, and it was pulled out of the mold.

Once the silicone molds were complete, it was used to create wax models of the object. Melted wax was poured into the mold and left to harden several times. The resulting wax models were retouched to more accurately reflect the original object and arranged in preparation to make a resin-bonded sand cast for metal casting.

Step 4: Wax Models

As mentioned above, melted wax was poured into the silicone molds to create wax replicas of the axe head. These replicas were placed together on sprues attached to paper cups. Straws were added to the blade of the axe to allow air to escape when bronze was poured.

There were four wax models made to increase the likelihood of a successful bronze pour.

Step 5: Resin Bonded Sand Cast Making

The wax replicas, sprueing, cups, and straws were packed in with resin-bonded sand. The resin and sand mixture hardens to create a sand cast. These sand casts will become the investments (molds that the metal is poured into). 

After the sand casts cured, the straws and cups were removed, so that the wax could melt out of the investment. 

Step 6: Lost Wax

The hardened sand casts were placed upside down in an oven to melt out the wax. The wax leaves cavities in the shape of the axe heads, into which the bronze is poured. 

Step 7: Bronze Pouring

The furnace has to heat the bronze in the crucible for a few hours before it is ready to pour. A pulley system is used to move the crucible out of the furnace. Slag (a mixture of impurities that rise to the top when metal is melted) is skimmed from the top of the melted bronze, and then the bronze is poured into the molds.

Step 8: Refining Replica

After the bronze cools and hardens, it is broken out of the sand casts. The sprues were cut off with a handheld band saw. The process of refining the axe heads was first started with hand filing; however, this was much too slow to be effective. One axe head was hand-filed to act as a comparison. An angle grinder was used to reshape and buff the other 3 axe heads.

Step 9: Final Axe Heads