WHAT IS PITCH?
Pitch is one of those ancient "basic" substances.
Most pitch was used for caulking boats and ships was made from tree sap, pine resin or "pine tar".
In metalwork it is the pliable backing that supports thin plate for repousse'.
Pitch is made a variety of ways.
Modern repousse pitch is made of a mixture of things including pine resin or asphalt tar, waxes and fillers like fine clay and sand.
The more and coarser the clay or sand fill the stiffer the pitch. The more beeswax the softer the pitch, other waxes can harden the pitch.
The heavier the work or the finer the detail the stiffer the pitch needs to be.
For some work in steel lead was used. Today soft zinc or tin is a better choice.
For heavy plate some smiths use compacted gravel, or an open support (no backing).
In standard work the pitch is melted and poured against the metal in a mold box or pitch bowl.
Then the metal is worked with various small hammers and punches the pitch supporting the work but moving out of the way where needed.
At some point the metal may become work hardened and need to be annealed.
The pitch is heated and removed, the metal heated to anneal then the pitch molded to the metal again.
This provides a new flat back surface and better support for the metal.
In some case the pitch is poured on the opposite side in this step so that the metal can be worked from the front. Work from the front is called "chasing".
Pitch is not necessarily used in armour work, even when repousse is involved.
Work in steel is often done against wood forms and lead as noted above.
In armour it would only be used for fine decoration, the bulk of the forming done by other methods.
See pitch recipes.
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