Conservation Report for the Bounty Cannon

This report details the work that has been done on the cannon to date. It is still undergoing treatment which is expected to continue for another few weeks. This is a fairly technical report as it has been written by our Conservation Office Janelle Blucher as part of our formal Condition Reporting regime. Despite its technical nature - it is still a really interesting report.

Conservation Report for The Bounty Cannon - September 28 2010
The initial objective was to remove a coating of Kephos primer, F & T Imperite 390 (polyurethane).  This coating was applied to the surface of the cannon 32 years ago . 

Description of Kephos Primer (sourced from supplier of product): Non – aqueous liquid chemical used undiluted (except for dip operations) to produce corrosion resisting, paint bonding coating on steel.  The paint grip coating when dry protects the surface from fingerprints, rust, etc. – usually for 6 months

Karina Acton of International Conservation Services tried to remove the coating with various solvents whilst on the island in 2008, eventually the only effective removal came about with the use of Selley’s Kwikstrip.  A sample of the coating was removed by Karina and taken back to I.C.S to further test for any other means of removal.  It was determined that the best option was to use Selley’s Kwikstrip.

One of the lockable sheds at the Administration works depot was set aside for the conservation area, this provided protection from weather and also salt air.  Lee Irvine from the Works Depot made a wooden cradle for the cannon to sit on whilst undergoing conservation.  The cannon was situated under a block and tackle which enabled a method of rotation for conservation purposes as well as being able to elevate at the cascabel end.

Conservation method -Week 1
Patch test 1 – Kwikstrip applied and left on the cannon for 5 minutes, then washed off resulted in no visible removal of coatings. 
Patch test 2 - Kwikstrip was left on the surface for 10 minutes, washed off resulting in some removal of coating, what appeared to be approx. 25%.
Patch test 3 – Kwikstrip was left of the surface for 15 minutes, washed off resulting in approx. 75%  removal of coating.

This satisfied any concern that the application of Kwikstrip was going to have any adverse affect to the surface of the cast iron and with repeated coatings of Kwikstrip the coating would eventually be removed. Proceeded to apply Kwikstrip working in sections throughout the day until entire surface had been treated twice over.  Left overnight to observe any changes to the cast iron being exposed.  A third application of Kwikstrip was painted on the following day and this appeared to remove the remainder of the coating. Brushed repeatedly with a nylon brush (dish brush) and washed repeatedly, final washes were with water collected from dehumidifiers (distilled water is not available). The exposed surface of the cannon had less corrosion than we anticipated, however approx 50% of the surface area did have superficial corrosion areas.  These spots were scraped with a scalpel and brushed with a soft wire (ferrous) brush.

Communication with Karina Acton: Emailed images of cannon to Karina and phoned to inform of the process and results at this stage.  The cannon obviously showing less corrosion than expected resulted in the decision to not immerse the object in a bath of caustic solution with electrolytic reduction process. She suggested using Citric Acid 5%/Thiourea 1% poultices on patches of corrosion.  These poultices were applied and left on for approx 15 minutes and then thoroughly washed off with water.  Mechanical and chemical removal of these superficial corrosion areas on the outside surface of the gun continued throughout the week.

Treating the bore:
The cannon was elevated approximately 20 degrees at the cascabel end.  A flat round wire brush was attached to the end of a steel rod which reached up to the end of the bore (approx. 2metres) this was used initially to scrape out the delaminated iron.  The wire brush and rod was attached to an electric drill and the inside heavily brushed to remove the flaking and delaminating material, a total amount of 263gms was removed.   Compressed air was blown through a hose attached to a rod which reached up to the end of the bore to remove all dust.

Thin metal tubing with holes punctured around the end was attached to a spray gun, this tube also reached to the end of the bore.  A substantial spray of methylated spirits was applied and allowed to dry.  The bore is clean and has a smooth surface except for one chunk of delaminating iron which would not come away, this piece is near the muzzle end of the gun and can be easily monitored and removed at a later time if necessary.    The same spray gun was then used to apply a substantial amount of Senson Rusticide (corrosion converter), this process was repeated twice and after examination with a light we could see a thorough application was achieved.  The bore did not have the coating of Kephos Primer and F & T Imperite 390 like the outside of the gun.

There was an unidentified coating around the circumference of the bore, approximately 2cm in from the muzzle and approx. 10cm in length.  It appeared to be wax, no solvent would remove it and Kwikstrip wasn’t having any affect.  Heat was applied to a patch with a hot air gun and this turned it white and sticky similar to chewing gum consistency. It appeared to be silicon, this was eventually removed mechanically with scalpel and wire brush and the area received its 2xcoatings of Senson Rusticide.  A coating of Senson Rusticide was painted on the whole outside surface of the gun on the Friday afternoon and it was left for 2 days.

Week 2
Continued working on areas of corrosion on outside surface of cannon using scalpel, soft wire brush and methylated spirits which removed most of the Rusticide that had been applied. It soon became very evident that microscopic pieces of the original coating still remained.  The surface of the gun is quite uneven and pitted and these small pieces of coating were embedded into the ‘pores’ of the cast iron. 

Communication with Karina Acton: Emailed images of cannon and informed Karina of these remaining small pieces of coating and she advised to return to further use of Kwikstrip until all had been removed.  Corrosion treatment would not reach the metal that was underneath these remaining pieces of coating.

Washed with water collected from dehumidifiers and brushed (nylon brush), dewatered (methylated spirits) and returned to Kwikstip application and removal.  Hot water was tried in some areas to maneuver the Kwikstrip into and out of the pores.  A scalpel was used to remove any stubborn coating that had been softened but not removed by Kwikstrip.  Repeated Kwikstrip process numerous times and washed, dewatered and brushed with nylon brush numerous times.  Superficial corrosion areas treated with the citric/thio poutices, localised ‘shaving’ with a scalpel, and soft wire brushing. Friday afternoon completed with an application (brushed) of Rusticide to the entire outside surface of the cannon.

Week 3: Removed Rusticide with dehum. water, dewatered (meths.) and brushed with nylon brush, applied Kwikstrip process to any further areas of remaining coating.  Brushing cannon with nylon brush after dewatering seemed effective in removing any microscopic flakes of loosened coating.   The cannon was continuously examined under artificial lights and sunlight when possible and a magnifying glass, finally satisfied that all of the original coating had been removed.  Fine ‘shaving’ of superficial corrosion areas still revealed a layer of fine ‘brown’ powdery corrosion.

Communication with Karina Acton: Karina was satisfied with amount of time spent working on the removal of the surface coating, her original observations of this coating had led her to believe that it would take approximately 2 weeks of continuous ‘work’ to remove it.  It was acceptable if 95% of the coating had been removed, a percentage that was certainly achieved. A fine layer of brown powdery corrosion products is acceptable and expected on the object.  Further treatment with citric acid/thiourea solution was recommended.  Senson Rusticide to be applied and object left for a few weeks for observation purposes prior to final sealing of the surface with Senson Ferroguard.

A fresh solution of 5% Citric Acid/ 1% Thiourea was prepared and brushed over the surface in sections until entire surface was treated.  This solution was applied 3 times and left on for 15 minutes each time (Approx. total of 450ml).   Repeated washing with dehumidifier water, brushing and dewatering and brushing again with nylon brush between each application. Senson Rusticide was brushed onto the surface of the cannon, a second coating was applied the following day. A blow up ball wrapped in my mylar was pushed into the muzzle of the gun to provide a seal for the bore. Once Rusticide had dried the cannon was covered loosely with mylar topped by a cotton cover  to keep off any dust.

Touch Hole: J. Carpenter 1987 WAMM report states that in 1977  “touch hole still to be drilled out (at present 2 inches  deep).” No known documentation states that it was ever drilled out.   Measurement now is a depth of 45mm which indicates this was never done. The touch hole was brushed with a thin nylon brush, washed, dewatered, paper was used a wick to draw out moisture and Rusticide filled the hole.

Core Sample Hole: This core sample was taken in the late 1970’s.  A small hole measuring 16mm remains at the side of the gun at the cascabel end.  Unable to fit nylon brush (width allows only a piece of tie wire to be inserted) otherwise received same treatment as the touch hole.