Peter%Mc%Elhinney1,%Nicole%Li3le2,%Benjamin%Ache3,%Brandon%Walters4%
%
1ConservaAon%Fellow,%Smithsonian%InsAtute,%NaAonal%Museum%of%the%American%Indian%
2Physical%ScienAst,%Smithsonian%InsAtute,%Museum%ConservaAon%InsAtute%
3ProducAon%Manager,%Micro%Photonics%Inc.%
4Laboratory%Manager,%Micro%Photonics%Inc.%
%
%
Presented%at%the%RATS%session%
42nd%Annual%MeeAng%of%
The%American%InsAtute%for%ConservaAon%of%Historic%and%ArAsAc%Works%(AIC)%
San%Francisco,%CA,%May%27RJune%1,%2014%
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The%research%I%am%presenAng%today%was%completed%as%part%of%the%Andrew%W.%Mellon%FoundaAon%Post%
Graduate%Fellowship%in%Object%ConservaAon%at%the%NaAonal%Museum%of%the%American%Indian%(NMAI)%in%
Washington%DC.%
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My%research%at%NMAI%focused%on%understanding%the%deterioraAon%mechanisms%of%Western%Red%Cedar%in%the%
collecAon%there.%Cedar%bark%is%well%represented%in%the%collecAon…%
Mc Elhinney, P., et al. 
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…%and%objects%are%oZen%accompanied%with%small%tags%marked%‘Inherently%Fragile.%Will%Have%ConAnued%Loss.’%
Being%an%inquisiAve%and%somewhat%stubborn%conservator,%I%decided%to%see%if%there%was%anything%I%could%do%to%
change%this%gloomy%forecast.%
%
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AZer%studying%the%material%for%some%Ame%I%concluded%there%were%gaps%in%our%understanding%of%this%material.%I%
decided%that%in%order%to%figure%out%a%treatment%protocol,%I%needed%to%understand%how%the%material%was%falling%
apart,%and%to%do%this%I%needed%to%be3er%understand%the%chemistry%and%microstructures%of%the%material.%Over%
the%following%year%I%improved%my%understanding%of%bark%materials%through%library%study%of%plant%biology,%and%
by%a3ending%workshops%like%the%NMAI%bark%materials%workshop%led%by%conservaAon%scienAst%Dr.%MaryRLou%
Florian,%pictured%here.%The%technical%approach%was%complemented%with%field%work%undertaken%in%Sitka,%
Alaska,%and%supervised%by%Tlingit%arAst%Teri%Ro_ar.%
%
I%should%confess%at%the%start%of%the%presentaAon%that%whilst%I%have%not%figured%out%how%to%treat%the%material,%I%
know%a%lot%more%about%why%it%falls%apart%than%I%did%when%I%started.%
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The%Western%Red%Cedar%is%an%evergreen%tree%from%the%Cuppressaceae%(Cypress)%family.%Trees%range%from%
about%65R70%meters%tall,%and%3R4%meters%in%diameter%with%the%oldest%known%tree%calculated%at%1460%years%old.%
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The%natural%range%of%the%tree%is%in%the%Pacific%Northwest%Coast%and%some%inland%areas%R%BriAsh%Columbia,%
Washington,%Oregon,%Northern%California,%Idaho%and%Montana.%Cultural%material%made%from%cedar%bark%can%
be%found%in%almost%all%of%the%cultures%associated%with%these%geographical%areas.%
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Western%Red%Cedar%is%a%li3le%unusual%in%that%it%doesn’t%have%a%true%bark%at%maturity.%The%tree%has%a%bark%layer%
in%the%first%few%years%of%growth,%but%the%wood%growth%rate%exceeds%that%of%bark%growth%rate%to%such%an%extent%
that%it%pracAcally%‘bursts%out%of%its%clothing’%as%the%tree%increases%in%girth.%
%
The%material%that%we%see%on%the%outside%of%the%mature%tree%is%actually%part%of%the%‘secondary%phloem’%layer,%
normally%involved%in%the%movement%of%nutrients%around%the%tree,%that%has%undergone%mechanical%and%
chemical%changes%to%help%protect%the%tree%from%the%outside%world.%
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Cells%produced%at%a%thin%layer%called%the%vascular%cambium%differenAate%toward%the%outside%of%the%tree%to%
become%phloem%cells,%whilst%other%cells%differenAate%toward%the%inside%of%the%tree%to%become%xylem%(wood)%
cells%(Beck%2010).%
%
The%secondary%phloem%layer%can%range%between%about%1/2%and%1%inch%in%thickness%(Dallimore%and%Jackson%
1967).%
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Looking%at%Western%Red%Cedar%phloem%under%the%microscope%can%be%a%li3le%confusing,%but%the%basic%Assue%
structure%is%beauAfully%%simple.%The%480x%scanning%electron%microscope%(SEM)%image%above%shows%a%small%
secAon%of%phloem%viewed%in%the%transverse%plane.%
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Elongated%fibers%with%thick%cell%walls%form%the%structural%scaffold%of%the%phloem.%The%cross%secAonal%shape%of%
these%cells%varies%from%thick,%almost%square%cells,%to%fla3ened%oblong%cells,%arranged%in%axially%aligned%rows.%
Mc Elhinney, P., et al. 
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Sieve%cells%are%distributed%in%rows%on%either%side%of%the%fiber%cells.%These%thinner%walled%cells%serve%as%the%pipe%
work%for%distribuAon%of%the%nutrients%and%metabolites,%moved%through%pores%concentrated%in%the%overlapping%
ends%of%these%long%slender%cells.%
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ThinRwalled%parenchyma%cells%are%distributed%between%the%rows%of%sieve%cells.%Cedar%phloem%parenchyma%
cells%play%a%role%in%storage%of%nutrients%in%the%form%of%starch%grains%visible%as%small%round%balls%in%the%SEM%
image,%but%may%also%contain%phenolic%compounds%responsible%for%regulaAon%of%growth,%signaling,%
pigmentaAon,%UV%radiaAon%screening,%and%defense%against%herbivores%depending%on%the%stage%of%phloem%
development.%
Mc Elhinney, P., et al. 
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When%we%look%at%cedar%phloem%in%three%dimensions,%we%can%see%that%in%addiAon%to%the%structural%
arrangement%described%previously,%nutrients%are%also%stored%and%distributed%through%ribbon%like%clusters%of%
conducAng%‘ray’%cells%arranged%radially%in%the%Assue.%
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In%this%image,%we%are%looking%at%a%small%secAon%of%what%would%be%a%conAnuous%ring%around%the%outside%of%the%
tree.%The%large%green%secAon%represents%the%wood,%the%red%secAon%the%cambium%(where%new%cells%are%
produced)%and%the%yellow,%brown%and%orange%squares%the%fiber,%sieve,%and%parenchyma%cells.%As%new%phloem%
cells%are%produced%at%the%vascular%cambium%layer,%older%phloem%cells%get%moved%toward%the%outside%of%the%
tree…%
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The%relaAvely%fast%growth%rate%of%the%wood%parts%of%the%tree%exerts%pressure%on%the%phloem%Assue,%(imagine%
the%phloem%layer%as%a%elasAc%band%around%the%increasing%girth%of%the%tree)%to%such%an%extent%that%the%thin%
walled%sieve%and%parenchyma%cells%in%the%outer%phloem%layers%are%crushed%and%distorted%(Beck%2010).%Whilst%
the%phloem%fiber%cells%become%increasingly%lignified%and%therefore%tougher%during%this%process,%the%crushed%
sieve%cells%are%no%longer%able%to%move%nutrients%around%the%tree%(Barton%and%MacDonald%1971).%Some%of%the%
parenchyma%cells%resist%compression%and%become%filled%with%phenolic%compounds.%%
%
These%chemical%and%mechanical%changes%contribute%to%the%Assue’s%funcAon%in%providing%protecAon%against%UV%
radiaAon,%weathering,%grazing%from%animals,%and%a3ack%from%insects%and%other%forms%of%bio%deterioraAon%
(Esau%1977,%Franceschi%et%al.,%1998).%Cedar%bark%objects%made%from%phloem%Assue%near%the%outside%of%the%tree%
will%have%stronger%fibres,%more%crushed%cells%between%these%fibres,%potenAally%making%it%come%apart%more%
easily,%and%increased%levels%of%phenols,%potenAally%making%them%more%resistant%to%UV%and%bio%deterioraAon.%
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One%of%the%be3er%understood%mechanisms%of%deterioraAon%for%Western%Red%Cedar%phloem%is%related%to%the%
close%associaAon%of%the%thickRwalled%fibre%cells%and%the%thinRwalled,%more%delicate%parenchyma%and%sieve%
cells.%Fractures%in%one%or%more%of%the%less%robust%parenchyma%or%sieve%cells%contribute%to%stress%
concentraAons%that,%as%the%cell%wall%fails…%
Mc Elhinney, P., et al. 
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…%are%transmi3ed%axially%along%the%row%of%cells,%eventually%contribuAng%to%porAons%of%Assue%cleaving%away.%
This%arrangement%of%weak%and%strong%cells%is%also%the%reason%why%cedar%splits%easily%along%the%width%of%the%
Assue,%a%trait%useful%for%preparing%the%material%for%producAon%of%cultural%material.%
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My%early%research%also%examined%the%role%of%pecAn%in%deterioraAon%of%culturally%processed%phloem%Assue.%
PecAc%materials%exist%as%a%gel%like%polysaccharide%distributed%in%some%cell%walls%and%throughout%the%
intercellular%spaces%in%Western%Red%Cedar%phloem.%PecAn%in%the%living%plant%is%negaAvely%charged%and%tends%
to%a3ract%Ca2+%and%other%posiAvely%charged%ions%(Cooper%1997)%such%that%it%is%someAmes%referred%to%as%
calcium%pectate%(more%on%this%later).%
%
While%li3le%has%been%wri3en%about%the%role%of%pecAn%in%culturally%processed%cedar%bark,%empirical%observaAon%
indicates%that%pecAn%gels%of%different%concentraAon%eventually%recrystallise%under%ambient%museum%
condiAons.%%
%
The%image%on%the%screen%shows%the%extent%of%crystallisaAon%of%small%gel%disks%aZer%about%one%month%in%the%
climaAcally%controlled%NMAI%conservaAon%lab.%It%seems%likely%therefore%that%the%dehydraAon%of%pecAc%
materials%in%dry%cedar%bark%will%impact%cellular%cohesion%to%some%extent.%In%other%words,%the%cellular%‘glue’%has%
dried%out.%
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I%wanted%to%visualise%the%changes%that%occur%across%the%width%of%the%phloem,%but%given%the%disrupted%nature%
of%some%cells%in%this%Assue,%found%that%physical%preparaAon%of%consistent%opAcal%microscopy%slides%was%
extremely%difficult.%
%
The%Western%Red%Cedar%phloem%photomicrograph%above,%given%to%me%by%Dr.%MaryRLou%Florian,%is%one%of%the%
best%images%I%have%seen%of%how%swollen%cells%impact%the%surrounding%Assue.%In%this%extremely%well%prepared%
slide,%the%swollen%cell%(possibly%a%radially%arranged%parenchyma%cell)%has%disrupted%what%would%have%been%at%
one%Ame%a%conAnuous%row%of%fiber%cells.%
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Some%of%my%NMAI%colleagues%had%been%experimenAng%with%computed%tomography%(CT)%scanning%as%a%means%
to%be3er%understand%what%goes%on%in%the%visually%inaccessible%parts%of%objects.%I%felt%that%this%nonRdestrucAve%
technique%had%potenAal%for%allowing%me%to%more%accurately%understand%what%was%going%on%within%the%
phloem%structure.%
%
The%resoluAon%on%the%Smithsonian%InsAtutes%medical%scale%CT%scanner%was%much%too%low%to%resolve%the%small%
Assue%structures%I%was%interested%in.%This%led%me%to%Micro%Photonics,%a%commercial%imaging%lab%in%Allentown%
Pennsylvania.%
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The%micro%CT%scanner%used%in%this%study%is%the%Bruker%Skyscan%1172,%pictured%here%in%the%Micro%Photonics%lab.%
The%sample%requires%no%special%preparaAon%before%being%mounted%by%gently%clamping%on%a%spindle%in%the%
scanning%chamber.%
%
I%won’t%go%into%too%much%detail%about%how%CT%scanning%works%in%this%paper%as%I’m%sure%many%of%you%already%
understand%this,%but%essenAally%the%scanning%device%produces%hundreds%of%twoRdimensional%‘slices’%though%
the%sample,%and%collates%these%using%computer%soZware%to%produce%a%three%dimensional%model.%The%model%
can%then%be%used%to%analyse%the%two%and%threeRdimensional%morphological%parameters%of%the%specimen.%
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The%video%above%is%a%threeRdimensional%rendering%of%the%cedar%bark%sample,%composed%from%twoRdimensional%
XRray%images,%stacked%and%arranged%using%Bruker&Skyscan&CT&Vol&soZware.%
%
The%sample%can%be%virtually%secAoned%in%any%plane,%and%while%this%is%useful%for%visualising%the%sample%shape%
and%volume,%the%1172%MicroCT%can’t%resolve%the%extremely%fine%cellular%structure%of%the%phloem%Assue%in%any%
useful%detail.%
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A%second%piece%of%soZware,%Skyscan&Dataviewer,%was%used%to%produce%this%video.%%
%
Here,%we%are%looking%at%a%cross%secAonal%view%of%the%phloem%structure,%oriented%with%the%inner%phloem%near%
the%top%of%the%screen,%and%the%outer%phloem%toward%the%bo3om.%The%soZware%allows%the%user%to%cycle%
through%hundreds%of%twoRdimensional%cross%secAon%images%produced%by%the%scanner,%revealing%Assue%
structure%pa3erns.%
%
The%large%bright%spot%that%appears%in%the%Assue%closest%to%the%vascular%cambium%(near%the%top%of%the%screen)%
at%about%30%seconds%was%somewhat%unexpected%but%interesAng%none%the%less.%This%bright%speck,%and%others%
like%it,%were%idenAfied%as%bioRmineral%crystals,%but%I%will%expand%on%this%later.%
%
As%the%video%progresses,%we%see%that%the%Assue%in%the%lower%secAon%of%the%screen%is%disrupted%at%various%
points%throughout.%I%believe%that%these%disrupAons%are%a%result%of%compression%of%the%outer%phloem%and%
swelling%of%phenol%filled%parenchyma%cells%described%previously.%
%
The%video%illustrates%that%even%across%a%very%narrow%cross%secAon%of%phloem%Assue,%we%see%considerable%
variaAon%between%relaAvely%wellRorganised%Assue%near%the%vascular%cambium,%and%the%disrupted%Assue%less%
than%5%mm%toward%the%outside%of%the%phloem%layer.%%
%
This%video%helps%us%visualise%how%objects%made%from%more%disrupted%Western%Red%Cedar%outer%phloem%might%
be%less%stable%during%handling%and%treatment%than%inner%phloem%objects.%
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I%wanted%to%see%if%I%could%put%some%numbers%to%the%visual%pa3erns%I%was%seeing%in%these%videos,%and%asked%the%
team%at%Micro%Photonics%to%run%some%analysis.%Analysis%was%performed%using%Bruker&CT&Analyzer&soZware%
which%uses%builtRin%algorithms%to%calculate%various%morphometric%parameters.%
%
Four%regions%of%interest%were%defined%by%virtually%‘shrink%wrapping’%four%naturally%occurring%secAons%of%the%
sample%labeled%in%the%image%above.%The%cell%wall%thickness,%and%volume%of%negaAve%space%within%each%region%
were%calculated%using%builtRin%algorithms%under%the%soZware%3D%Analysis%funcAon,%and%are%compared%in%the%
following%tables.%
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This%table%shows%the%results%of%measurements%of%average%cell%wall%thickness%across%the%4%regions%shown%on%
the%previous%slide.%
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As%we%can%see%from%the%table,%there%is%li3le%detecAble%variaAon%in%the%average%cell%wall%thickness%between%
regions%1R3.%
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The%cells%in%region%4,%(the%area%closest%to%the%vascular%cambium)%have%a%significantly%higher%average%thickness%
than%those%in%regions%1R3.%This%is%most%likely%influenced%by%the%high%number%of%cells%in%this%region%with%not%yet%
fully%developed%intracellular%spaces.%%
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This%table%shows%the%results%from%measurements%of%negaAve%spaces%within%the%four%phloem%regions.%
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The%table%shows%that,%although%regions%1R3%have%very%similar%amounts%of%negaAve%space%as%a%percentage%of%
the%total%Assue%volume…%
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…the%average%size%of%each%discreet%area%of%negaAve%space%in%region%1%is%larger…%
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…than%in%regions%2%and%3,%and%%significantly%larger%than%in%region%4.%
%
The%larger%areas%of%negaAve%space%within%region%1%may%make%this%material%less%suitable%for%the%producAon%of%
fine%grade%cultural%material%than%that%in%regions%2R4.%In%simple%terms%the%bark%in%region%1%has%bigger%holes%in%it.%
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One%of%the%more%unexpected%results%of%CT%scanning%this%material%was%the%visualisaAon%of%relaAvely%dense%
material%distributed%throughout%the%bark.%%
%
The%model%above%has%been%produced%using%the%same%Skyscan&CT&Vol%soZware%described%previously,%with%the%
senngs%adjusted%to%represent%only%the%most%dense%material%within%the%Assue.%
%
The%video%on%this%slide%goes%some%way%to%illustraAng%the%number%and%distribuAon%of%dense%materials%
(represented%by%white%specks),%which%turn%out%to%be%bioRminerals,%within%the%bark%structure.%BioR
mineralizaAon%is%the%precipitaAon%of%minerals%as%a%result%of%the%metabolic%funcAoning%of%a%living%organism,%
and%is%widely%pracAced%by%plants.%PlantRAssue%biominerals%are%overwhelmingly%of%three%chemical%types:%
calcium%oxalate,%silica,%and%calcium%carbonate.%Of%these%types,%calcium%oxalate%is%thought%to%be%the%most%
prevalent%and%widespread.%
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This%video%was%produced%using%the%Skyscan&Data&Viewer&soZware%described%previously.%
%
In%this%video%we%are%looking%at%a%transverse%view%of%the%phloem%Assue%with%colours%assigned%to%the%different%
pixel%density%values.%In%this%case,%blue%and%white%pixels%represent%the%most%dense%material%within%the%Assue,%
while%yellow%and%red%colours%the%least%dense%material.%
%
As%we%cycle%through%the%twoRdimensional%images,%distribuAons%of%blue/white%coloured%dense%material%appear%
to%flow%from%the%Assue%nearest%the%vascular%cambium%toward%to%the%Assue%closer%to%the%outside%of%the%tree,%
giving%us%a%much%clearer%idea%of%how%the%bioRminerals%are%distributed%throughout%the%phloem.%Of%course%the%
material%is%not%‘flowing’,%but%if%we%translate%this%into%a%threeRdimensional%volume,%it%would%be%distributed%in%
gently%sloping%radiallyRarranged%channels%(running%from%the%inside%to%the%outside%of%the%plant)%in%much%the%
same%orientaAon%as%the%phloem%rays.%
%
The%video%also%indicates%flushes%of%dense%material%in%associaAon%with%areas%of%disrupAon.%It%is%unclear,%but%
interesAng%to%speculate%about%whether%this%material%is%contribuAng%to%dehiscence%in%these%areas%(splinng%at%
maturity%along%a%builtRin%line%of%weakness%in%a%plant%structure%in%order%to%release%its%contents).%
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The%sample%material%was%examined%using%scanning%electron%microscopy%with%energy%dispersive%spectroscopy%
(SEMREDS)%to%help%characterise%the%relaAvely%dense%material%within%the%phloem%structure.%
%
As%we%can%see%in%the%series%of%images%above,%white%specks%of%material%in%the%intercellular%spaces%agree%with%
the%distribuAon%of%dense%material%observed%in%the%previous%video.%
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Using%EDS%mapping,%we%see%calcium%detected%in%correlaAon%with%the%white%material.%The%associaAon%of%Ca2+%
ions%with%negaAvely%charged%pecAn%makes%it%difficult%to%disAnguish%between%the%distribuAon%of%calcium%
pectate%and%calcium%oxalate%using%EDS%mapping%alone.%
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When%we%look%at%the%white%material%in%more%detail%we%can%see%that%what%appear%to%be%amorphous%globs%are%
in%fact%made%up%of%clusters%of%small%shardRlike%crystals.%The%individual%crystals%in%this%image%measure%in%the%
region%of%1R2%microns%in%diameter.%Again%using%EDS%mapping,%we%can%see%that%the%rhombohedral%and%
tetragonal%crystals%map%closely%for%calcium%and%oxygen,%suggesAng%that%they%are%likely%calcium%oxalate.%
%
A%2003%study%that%examined%distribuAon%of%calcium%oxalate%in%different%conifers%(Hudgins%et%al%2003)%agrees%
with%the%distribuAon%in%our%sample,%with%calcium%oxalate%most%abundant%between%radial%walls%of%all%cell%types,%
and%generally%embedded%in%and%enveloped%by%cell%wall%material.%The%study%also%concludes%that%there%are%
higher%concentraAons%of%crystals%in%the%middle%and%outer%phloem%than%in%the%inner%phloem%Assue,%and%that%
some%members%of%the%Curprassaceae%family%have%10R20%Ames%the%amount%of%CaOx%as%are%found%in%other%
conifers.%%
%
The%large%volume%and%widespread%distribuAon%of%calcium%oxalate%in%Western%Red%Cedar%phloem%may%well%be%a%
contribuAng%factor%in%the%deterioraAon%by%cell%wall%abrasion%of%cultural%material%made%from%this%Assue.%Some%
of%the%abrasive%acAon%is%likely%miAgated%in%the%living%plant%as%the%crystals%are%distributed%within%a%pecAc%gel%
matrix,%but%as%the%pecAc%material%crystallises%in%harvested%and%processed%phloem,%the%lubricaAng%acAon%of%the%
pecAn%is%greatly%reduced.%The%higher%distribuAon%in%middle%and%outer%phloem%Assue%may%indicate%increased%
abrasive%acAon%in%cultural%material%made%from%these%parts%of%the%phloem.%
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When%we%look%at%the%more%wellRdefined%crystals%using%the%SEM%we%can%see%that%these%crystals%are%much%larger%
RR%between%10%and%20%microns%in%diameter%RR%and%have%a%less%regular%shape%than%the%smaller%calcium%oxalate%
crystals.%Using%EDS%we%can%see%that%the%crystals%are%formed%from%aluminum%(green),%Atanium%(yellow),%
potassium%(purple)%and%silicon%(blue)%and%are%likely%silicate%biominerals%formed%in%combinaAon%with%metal%
ions%absorbed%from%the%surrounding%soil.%
%
While%these%crystals%are%much%less%abundant%than%the%calcium%oxalate%crystals,%their%relaAvely%large%size%could%
be%enough%to%induce%localised%stresses%necessary%to%iniAate%the%axial%cleavage%mechanism%described%
previously,%contribuAng%to%delimitaAon%of%layers%of%phloem%Assue.%
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I%had%hoped%to%use%the%Bruker%analyAcal%soZware%to%map%the%number%and%distribuAon%of%crystals%within%the%
phloem%Assue.%While%this%‘bright%speck%analysis’%funcAonality%exists%within%the%soZware,%the%resoluAon%of%the%
scans%was%too%low%to%accurately%detect%the%extremely%small%individual%calcium%oxalate%crystals.%The%1R2%micron%
diameter%crystals%are%smaller%than%the%individual%3.77%micron%pixels%size%selected%for%these%scans.%
%%
I%am%currently%making%arrangements%to%have%cedar%sample%analysed%at%Skyscans%Laboratory%in%Belgium%where%
they%have%a%relaAvely%new%unit%RR%the%2011%xRray%nanotomograph%RR%with%spaAal%resoluAon%in%the%range%of%
hundreds%of%nanometers%(1million%nm%=%1%mm).%%
%
Some%research%into%the%size%and%scale%of%perAnent%features%of%sample%material%can%be%helpful%in%selecAng%the%
appropriate%scanning%techniqueR%CT,%MicroRCT,%to%NanoRCT.%
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Whilst%some%of%these%findings%may%seem%abstract,%they%have%implicaAons%for%the%conservaAon%of%Western%Red%
Cedar%bark%material%objects.%Hilary%Stewart%(Stewart%1984)%menAons%a%processes%of%‘grading’%cedar%bark%aZer%
harvest%by%splinng%the%thickness%of%the%harvested%phloem.%Further%invesAgaAon%of%this%process%may%help%
refine%the%currently%used%terms%‘inner’%and%‘outer’%phloem.%%
%
Cedar%bark%objects%in%the%collecAon%of%NMAI%range%from%material%that%appears%to%be%made%from%very%fine,%
well%ordered%phloem%consistent%with%that%observed%near%the%cambium,%while%other%objects%appear%to%be%
made%from%a%‘rougher’%grade%of%phloem%material.%%
%
Further%research%is%required%to%gain%a%be3er%understanding%of%how%much%of%the%phloem%harvested%from%the%
tree%is%used%to%produce%cultural%material.%How%do%harvesters%and%makers%determine%the%inner/outer%Assue%
boundaries?%How%are%different%parts%of%the%phloem%Assue%used%for%different%applicaAons?%
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This%research%concludes%that%cultural%material%made%from%phloem%Assue%close%to%the%cambium%in%the%living%
tree%may%have%quite%different%properAes%to%material%formed%from%phloem%Assue%in%relaAvely%close%proximity%
(Hudgins%et%al%2003).%DisrupAon%of%sieve%and%parenchyma%cells,%observed%in%the%outer%but%not%the%inner%
phloem,%will%likely%impact%the%structural%stability%of%cultural%materials%made%from%these%Assues.%
Likewise%abrasion%associated%with%increased%accumulaAon%of%calcium%oxalate%crystals%in%outer%phloem%Assue%
may%result%in%increased%cell%wall%damage%during%manipulaAon%of%some%bark%objects%during%treatment%and%
handling%for%exhibit%and%storage.%The%higher%concentraAon%of%extractable%phenols%in%Western%Red%Cedar%
outer%bark%versus%inner%bark%indicate%that%inner%bark%material%objects%may%be%more%suscepAble%to%damage%
from%UV%and%biological%deterioraAon%than%those%made%from%outer%bark%Assue%(Franceschi%et%al.,%1998,%
La3anzio%et%al.,%2006).%This%needs%to%be%considered%in%relaAon%to%storage%and%display%of%these%types%of%
objects.%
%
Whilst%I%agree%that%these%conclusions%do%not%necessary%solve%the%problems%that%I%iniAally%set%out%to,%I%believe%
they%bring%us%one%step%closer%to%understanding%where%to%begin.%Beyond%my%current%research%commitments,%I%
would%like%to%correlate%what%I%have%learned%about%this%unique%material%with%condiAon%issues%observed%in%
museum%collecAons,%and%eventually%draw%up%a%list%diagnosAc%features%and%treatment%protocols%for%the%
different%types%of%phloem%Assue.%%
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