Title: In situ protection and conservation of the Zakynthos wreck
First published: 1999
Description: ABSTRACT

Over  the  last  40  years  a  large  number  of  shipwrecks  have  been  recorded  around  the  world. Recently,  the  preservation  of  several  historic  wooden  ships,  has  highlighted  the  work  of  maritime  archaeology  and  provided  public  access  to  important  finds  of  cultural  heritage.
The  aim  of  this  study  was  to  investigate  the  preservation  of  the  Zakynthos  wreck  (Greece). 
The  first  part  of  the  work  investigated  the  protection  of  the  wreck  timbers  during  and  after  excavation  and  the  second  part  the  most  appropriate  method  for  their  conservation.

In  order  to  understand  the  processes  that  contribute  to  the  preservation  and  degradation  of the  Zakynthos  wreck  material,  the  ecology  and  nature  of  the  pelagic and  benthic environments  of  the  Zakynthos  site  were  investigated. Data  obtained  from  12  months  monitoring  of  the  site  showed  a  normal  marine  open-circulation  environment  with a high  biodeterioration  risk. Major  deteriogens  were  molluscs,  and  to  a  lesser  extent  crustacean  borers  and  lignicolous  fungi. Pine,  beech  and  oak  samples  exposed  for  24  months  at  the  site  showed  high  deterioration  rates. Physico-chemical  and  microbiological  analyses  of  the  benthic  environment  showed  it  to  be  a  sandy,  low  energy  anaerobic  sediment. Based  on  this  information,  an  in  situ  protection  method  for  the  timbers  exposed  during  and  after  excavations  was  developed.

The  geotextile  “Terram”,  a  synthetic  product  made  of  polyethylene  and  polypropylene,  was  tested   in  vivo  at  Zakynthos  and  Langstone  Harbour  (UK)  and  in  vitro  for  its  suitability  as  a  physical  barrier  system  against  marine  boring organisms. Four  different  grades  of  Terram  were  used : 500,  1000,  2000  and  4000,  and  controls. Terram  grades  2000  and  4000  provided  effective  protection  against  marine  borer  infestation  in  both  laboratory  and  field  studies. In  situ  application  of  Terram  4000  at  the  Zakynthos  site  demonstrated  the  mechanical  resistance  of  the  fabric  and  its  stability  in  the  marine  environment. After  one  year  the  geotextile  was covered  by  sand  and  colonised  by  marine  fauna  and  flora. It  returned  the  excavated  site  to  a  stable  anaerobic  environment  and  ensured  the  protection  of  shipwreck  timbers  buried  within  it. Terram  4000  is  recommended  for  the   in  situ  protection  of  wreck  timbers  in  marine  archaeological  sites.

The  majority  of  the  archaeological  material  found  at  Zakynthos  site  was  waterlogged  wood  and  the  extent  of  its  degradation  affects  significantly  its  conservation. Characterisation  of  the  degree  of  deterioration  of  the  oak  timbers  encountered  at  the  Zakynthos  shipwreck  was  determined  by  examination  of  their  micro-morphological  and  physico-chemical  properties. The  preservation  condition  of  oak,  pine  and  birch  samples  from  the  Mary  Rose  wreck  was  also  determined  in  order  to  obtain  a  wider  range  of  wood  species  and  conditions. 

A  comparative  study  of  conservation  treatments  involved  three  low  (PEG 200, BREOX  50A20,  BREOX 50W200)  and  two  high  (PEG  4000,  BREOX 50W4000)  molecular  weight  water-borne   polymers. These  were  tested  in  a  one-  and  two-stage  impregnation  systems,  followed  either  by air  or  freeze  drying. In  the  one-stage  impregnation  system  followed  by  air  drying  BREOX 50A20  and  BREOX 50W 4000  were  found  to  be  unsuitable. PEG  200  provided  consolidation  to  the lightly  degraded  samples  and  PEG  4000  to  the  heavily  degraded  ones. Polymer  content  estimated  for  the  low  molecular  weight  chemicals  showed  that  PEG 200  was  retained  to  a  greater  extent  than  either  BREOX 50A20  and  BREOX 50W200. When  BREOX 50A20  was  used  as  a  pre-treatment  to  freeze  drying  in  a  one-stage  impregnation  system  it  provided  effective  consolidation  for  waterlogged  wood  and  gave  better  aesthetic  results  than  either  PEG  200  or  BREOX  50W200. Samples  treated  with this  polymer  also  displayed  very  low  values  of  moisture  content  at  the  equilibrium  state. 

In  a  two-stage  treatment  system   followed  by  air  drying,  BREOX 50A20  showed  compatibility  with  PEG 4000  and  displayed  the  best  ASE  for  oak  and  pine  samples. Similar  ASE  values were  exhibited  by  PEG,  BREOX 50A20  and  BREOX 50W200  in a  two-stage  system  followed  by  vacuum  freeze  drying. Finally,  all  hardwoods  examined  displayed  better  ASE  values  in  all  impregnation  systems  when  followed  by  vacuum  freeze  drying  rather  than  air  drying. 
In  conclusion,  the  results  of  this  study  indicated  that  Terram  4000  is  an  effective  physical  barrier  system  for  the  in  situ  protection  of  excavated  wreck  timbers. Furthermore,  they indicate  that  if  the  Zakynthos  wreck  is  to  be  conserved  as  a  complete  structure,  a  two-stage  impregnation  system  followed  by air  drying  using,  BREOX 50A20  and  PEG 4000  is  the  preferred  treatment. Conversely,  if  the  wreck  is  be  conserved  as  separate  timbers  and  then  reassembled,  PEG 200  or  BREOX 50A20  used  in  a  one-stage  impregnation  system  followed  by  freeze  drying  is  the  most  appropriate.
Subjects: Maritime archaeology, Shipwrecks, Shipwreck conservation