Friday, 28 March 2003 00:00

Artifact Restoration for the Layman

By Trevor Jackson - Esperance Star

If you dive wrecks on a regular enough basis, sooner or later you're probably going to discover an artifact that you'll want to take home as keepsake. Unless you are the actual owner of the ship you are diving, you will probably be breaking the law in some way by doing so. The fact that a ship or object is on the bottom of the sea does not change the laws of ownership. If I drop my wristwatch over the side of the boat it still belongs to me, regardless of who finds it or who retrieves it. If my ship sinks, it is still my responsibility if it causes pollution or damages another boat. It is also still my property or the property of my representative, an Insurance company for example. Very old ships are either the property of an insurance company or the govt. and in some rare cases an overseas govt or entity. For example the US Navy still claims ownership of all its property no matter what it is or where it is located, hence the 'Dolphin', wrecked near Noosa during World War 2 would fall under that foreign ownership category. There are many grey areas here, but rest assured, whatever you take belongs to someone else.

Part 1

Notwithstanding all of that, it would be hypocritical of the author to suggest that the reader adopts the 'look but don't take' approach. So assuming you've got something you want to keep, lets discuss some basic preservation techniques that may help keep that treasure in tip top condition.

Firstly it must be made clear that the preservation of any article begins at the wreck site itself. Objects brought up from the sea floor will begin to deteriorate immediately if they are allowed to dry out. Salt deposits that have formed under the surface of the artifact will almost instantaneously start to crystallize upon reaching the surface. This process is helped along in no small amount by the absence of moisture and to a lesser degree the reduction in pressure. Often objects that have been immersed on a wreck site for many years have become stabilized in their marine environment and deterioration has been slowed to a minimum. Rapid stressful changes in that environment in terms of temperature, moisture, pressure and the availability of oxygen need to be controlled so as to reduce any acceleration in the deterioration process. Where possible, small items like bottles, vases and metal fittings should be placed in a secure container whilst still underwater. Attention should be given when actually picking up artifacts. Take careful note of where the artifact was located with regard to the rest of the wreck. It can be disconcerting to find 'one of a set' of something then realize later on the surface that you have no idea where you found it. Artifacts like compasses or sextants may indicate where the bridge of an old ship was, and further artifacts of the same ilk may be found if care is taken to record the position of the find. Care must also be taken against any physical damage. Glass and ceramic ware can easily be broken and is often reduced to useless rubble by overzealous treasure hunters. A diver trying to wretch that old bottle from its encrustations could easily end up with a bottle in two halves That two inch thick iron shackle may be as brittle as a matchstick, it may snap if even the slightest pressure is applied .Kid gloves are appropriate no matter what the material.

If the artifact is say an anchor or a bell and can't be placed in a container underwater, try to reduce to a minimum its exposure to the atmosphere once on the surface. Wet towels, blankets or Hessian bags can come in handy here but preferably your artifact would be re-immersed in a large container on deck. Failing that, wrap the piece well and keep it damp at all times.

Materials immersed in seawater, whether they are the hull plates of a ship, the pylons of a jetty or ancient ceramic vases will begin to deteriorate from the moment of immersion. This deterioration can take several forms and your recovered artifact may suffer from one or all of them. Firstly we have biodeterioration, where marine borers or microorganisms attack materials of an organic nature. Most wooden hulled wrecks you may find yourself on are all but completely decayed. A casual dig in the sand or mud will sometimes reveal pieces of wood, but in almost all cases in wooden wrecks of even moderate age, say 20 years, the hull is gone. On older wrecks, material of an organic nature like bone, leather, wood, fabric or paper will probably only be located by carefully removing the seabed sediments around the wreck site. At one location on the wreck of the Aarhus near Brisbane, the movement of sand during some heavy storms in 1999 revealed timber cases that contained a shipment of books, medical journals in fact. Although organic in makeup, these books and cases had been preserved by a combination of being drenched in kerosene at the time of the ships sinking, and by the fact that they had the protection of several feet of clean sand above them, keeping the borers and bacteria at bay. These 105-year-old books were in such fine condition that the pages could be easily read, but their removal from the wreck by anyone but an expert would surely have meant their demise.

The second form of deterioration is mechanical or physical abrasion. Basically this entails shipwrecks and artifacts being worn by the action of waves surge and current, or destroyed by the interaction of man. Like biodeterioration, artifacts buried in the seabed fare better than those exposed to the elements. Little can be done to reverse the results of physical abrasion; it's very much a case of the horse having bolted. The key here is to prevent the horse bolting by not opening the gate yourself. As previously mentioned, take care on the site when removing artifacts, maintain good buoyancy when moving close to the wreck, and if you are the boat skipper, take care when anchoring.

It is with the third and final form of marine deterioration, corrosion, that amateur artifact preservers will be most concerned. The reason for this is that most artifacts recovered from wrecks by recreational divers are of composed of some type of metal, usually brass, but occasionally iron, steel or even gold and silver. With the exception of gold, most metals found on shipwrecks will be the victims of corrosion to some degree.

Part 2

Iron

On ships constructed prior to the 1900s, all ferrous metals were either cast iron or wrought iron. Cast iron artifacts such as cannons and cannon balls contain higher concentrations of carbon than do wrought iron artifacts like anchors, nails and machinery parts. The carbon in cast iron takes the form of graphite flakes that form a network throughout the metal. When immersed, cast iron artifacts corrode from the outer layer inwards, the iron being corroded away and leaving a carbon rich surface layer surrounding an uncorroded iron rich core within. This carbon is present as the mineral graphite, and this layer can often retain exceptional surface detail of the artifact. This outer carbon layer, being of a different composition to the inner core of the artifact, is prone to 'onion skinning' off, if not treated properly.

Wrought iron contains a negligible amount of carbon and more often than not does not maintain its surface integrity very well. The surface of a wrought iron piece will corrode along lines of slag inclusions formed when the iron was folded, hammered and forged into its final shape. This surface after it has corroded can take on a grooved wood grain appearance and will rarely retain any surface detail. Again the surface of wrought iron can onionskin off if not treated correctly.

Despite the differences in their chemical composition, cast iron and wrought iron require the same treatment. The main aim here is to rid the metal of salt, whilst preventing it from corroding further, so start by maintaining the artifact in an immersed state. After transporting the artifact to a place where it can remain undisturbed for about a year, make up a solution of about 2% caustic soda. If you are dealing with a large artifact this will mean lot of caustic soda in a very large container. A cannon for example may pose a bit of a problem. One solution to this is to dig a small pool in your back yard using a tarpaulin or thick plastic as a liner. This of course would require some considerable dedication, remembering that caustic soda is a potentially dangerous chemical and that it will take a long time to complete the restoration process properly. Caustic soda is used to raise the ph level of the liquid in which the artifact is being desalinated. At a ph level above 12, the corrosion in iron is all but halted. If the ph level falls below this, the iron piece may deteriorate further whilst being desalinated. Throughout this process, the ph and salinity levels of the liquid should be recorded at monthly intervals. Should the liquid require topping up due to evaporation, these levels should be recorded at that time also. When the level of salinity reaches a plateau, change the liquid completely and repeat. Once the salinity has balanced out again, your piece should be stable enough to remove from the liquid.

It is possible to speed up this process by adding electrodes to the liquid and the artifact, but this requires careful monitoring and can quickly go astray if you don't know what you're doing .It is also imperative not to accidentally set up an electrolytic action by placing two dissimilar metals [like copper and iron] in the same container. Its probably also worth mentioning that iron objects can be desalinated using just fresh water alone and good results can be achieved at the expense of some minor further corrosion. This corrosion will take the form of a rusty orange silt forming on the outside of the artifact, the kind of silt you may kick up inside a wreck. For very large artifacts it may be safer to simply immerse them in straight fresh water and eliminate the worry of having large amounts of caustic soda solution lying around in the yard.

Copper, Brass and Bronze

Professional marine archeologists would argue that like iron; copper and its alloys are quickly corroded in seawater. In a long-term sense this is true, however because most of the wrecks we dive in Australia are say less than 100 years old, copper brass and bronze artifacts are often found in remarkable condition despite their time underwater. For divers who collect items from wrecks, these metals are in the majority of cases, the most prized and the most commonly found and restored. Solid brass artifacts with unpolished surfaces like propellers or engine plates need little attention, a few months in fresh water would almost be considered overkill. Most copper alloys that have been immersed for some time display the effects of what is known as bronze disease. Bronze disease is similar to corrosion in iron but instead of normal rust forming it takes the outward appearance of a green powdery discoloration on the surface of the metal. It is however far less volatile than rust in iron and will not usually result in the item disintegrating from within as can happen with dried out iron objects [onion skinning]. Most brass or bronze in the authors' collection have received little or no treatment and have no real ill effects from this neglect. It would however be prudent to show a little more concern with copper or brass items that do have a polished surface.

The ships Telegraphs from the Kaptjain Neilsen found last year have highly polished surfaces. They were in the water for about 35 years and were highly encrusted when brought to the surface. Be very careful when handling items like these that you don't get overzealous and start chiseling barnacles away with metal tools and destroying the surface of the artifact. A gentle and patient hand is required here. A very light solution of hydrochloric acid can be useful in removing encrustations. Remember that there is no real rush, a solution of 2% or less can be quite effective over a week or so. The use of higher concentrations can result in the surface of the metal being aggressively pitted as the acid finds weaknesses and gouges them out. These telegraphs were in solution for about 5 days before being removed and gently deconcreted by a very patient hand. A further 5 to 7 days in the acid bath would have done them no harm whatsoever. Bicarbonate of Soda could also be used to help soften this type of concretion, though its use is probably more appropriate on glass and earthenware surfaces that require an even more gentle touch.

Glass and Pottery

Compared to almost all forms of metal, ceramics and glass are the great stayers in the underwater environment. Ceramic vases fired before the birth of Christ are commonly found in a perfect state of preservation, sometimes by the shipload. It's unlikely that any ceramic ware of that vintage exists underwater off the coast of Qld, but many of their younger cousins may. I would say however that, of all artifacts you might find these require the most rapid treatment. By that I mean that removing them from the water will instantly affect the surface. If you observe a kind of rainbow effect on the surface of the material it may already be too late, damage has already begun. The trick with these items is to remove them from the water without actually removing them from the water. Put them in a bucket first before lifting from the sea. When you get them home place them in a larger container of fresh water and put the hose in it till it runneth over. This will mean that the article has never felt the dry air and the delicate surface should remain intact. To obtain a near perfect result, leave them immersed for a year, then dry them out in a very humid environment over a few months. One technique for achieving this is to leave the article in a bucket with just an inch or two of water in it. Cover the piece with a wet rag and place in a dark confined area. The rag will act as a wick and draw the moisture up from the bucket and should keep the surface of your artifact relatively wet. After a few months in this condition you should have an artifact that is stable and completely restored, ready for the 'poolroom'.