20
ARTÍCULO / ARTIGO / ARTICLE
CONSERVAR PATRIMÓNIO 36 (2021) 20-35 · h ps://doi.o g/10.14568/cp2019037 · ISSN 2182-9942
ARP · Associação P o issional de Conse ado es-Res au ado es de Po ugal · h ps://conse a pa imonio.p
AINARA
ZORNOZA-INDART 1 *
PAULA LOPEZ-ARCE 2,3
LUCÍA LÓPEZ-POLÍN 4
1. Depa men o Pain ing,
Facul y o Fine A s, Uni e si y
o he o he Basque Coun y
(UPV/EHU), Lejona, Spain
2. Uni e si y College
London (UCL), Ins i u e o
En i onmen al Design and
Enginee ing (IEDE), The
Ba le , School o En i onmen ,
Ene gy and Resou ces, Facul y o
he Buil En i onmen , London,
Uni ed Kingdom
3. P ope y Ca e Associa ion,
Camb idgeshi e, Uni ed
Kingdom
4. Ins i u Ca alà de
Paleoecologia Humana i
E olució Social (IPHES), Zona
Educacional, Ta agona, Spain
* aina a.zo [email protected]
A chaeological che a i ac s om A apue ca
si es (Bu gos, Spain): cha ac e iza ion,
causes o decay and selec ion o compa ible
consolida ing p oduc s
A e a os a queológicos de che e de A apue ca
(Bu gos, Espanha): ca ac e ização, causas
de de e io ação e seleção de p odu os de
consolidação compa í eis
Abs ac
Che ools om Gale ía and G an Dolina Ca es, loca ed in he Sie a de A apue ca si e complex
(Bu gos, Spain), we e cha ac e ized (mac o- isual inspec ion, mine alogical phases, deg ee o
c ys allini y, soluble sal s, su ace mo phology and op ical su ace oughness) and compa ed
o che samples collec ed om he su ounding A apue ca moun ain ange. The che ools
we e s udied o de e mine hei causes o decay and o selec ing he mos compa ible conso-
lida ion ea men s. I was ound ha samples solely con aining qua z we e no signi ican ly
al e ed and equi ed li le conse a ion ea men compa ed o hose ha con ained qua z
and mogani e, which we e mo e wea he ed and powde y, equi ing consolida ion. The e i-
cacy o he consolida ing p oduc s adi ionally used by conse a o s (ac ylic esin and e hyl
silica e) o p ese e hese che emains, oge he wi h no el nanopa icle-based p oduc s
(SiO2 and a mix u e o SiO2 and Ca(OH)2 nanopa icles) we e assessed in his s udy. Changes
p oduced by hese consolida ing p oduc s in he physical (su ace mo phology and cohesion)
and aes he ic p ope ies o he che ools we e e alua ed using non-des uc i e echniques
(peeling es , spec opho ome y and op ical su ace oughness), ollowed by des uc i e ech-
niques, such as SEM and XRD.
Resumo
Os u ensílios de che e das g u as Gale ía e G an Dolina, localizadas no complexo da
Sie a de A apue ca (Bu gos, Espanha), o am ca ac e izados (inspeção mac o- isual, ases
mine alógicas, g au de c is alinidade, sais solú eis, mo ologia da supe ície e ugosidade
óp ica da supe ície) e compa adas com amos as de che e ecolhidas na co dilhei a de
A apue ca. Os u ensílios o am es udados pa a de e mina as causas de de e io ação e
seleciona os a amen os de consolidação mais compa í eis. Ve i icou-se que as amos as
con endo exclusi amen e qua zo não o am signi ica i amen e al e adas e exigi am pouco
a amen o de conse ação em compa ação com as que con inham qua zo e mogani e, que
es a am mais al e adas e pul e ulen as, exigindo consolidação. Nes e es udo oi a aliada a
e icácia dos p odu os de consolidação adicionalmen e usados pelos conse ado es ( esina
ac ílica e silica o de e ila) pa a p ese a os es os de che e, jun amen e com no os p odu os
baseados em nanopa ículas (SiO2 e uma mis u a de nanopa ículas de SiO2 e Ca(OH)2). As
al e ações p oduzidas po es es p odu os consolidan es nas p op iedades ísicas (mo ologia
e coesão da supe ície) e es é icas o am a aliadas po écnicas não des u i as ( es e de
descamação, espec o o ome ia e ugosidade da supe ície óp ica), e des u i as, como
SEM e DRX.
PALAVRAS-CHAVE
A e a os a queológicos
de che e
Consolidação
Nanossílica
Nanopa ículas de
Ca(OH)2
Resina ac ílica
Silica o de e ilo
KEYWORDS
A chaeological che
a i ac s
Consolida ion
Nanosilica
Nanolime
Ac ylic esin
E hyl silica e
ARTICLE / ARTIGO
21 CONSERVAR PATRIMÓNIO 36 (2021)
A. Zo noza-Inda , P. Lopez-A ce, L. López-Polín
In oduc ion
Che is a sedimen a y c yp oc ys alline siliceous ock
p ima ily composed o qua z (SiO2) and o he silica e
mine als like mogani e, opal, o clay o ca bona es and
o ganic ma e ial, which a e conside ed impu i ies [1].
The in insic p ope ies o che , such as ha dness and
conchoidal ac u e, had made i widely used as a aw
ma e ial o knapping h oughou he his o y o mankind.
Al hough i is a du able ma e ial, che a i ac s a e o en
ound in poo conse a ion condi ions in a chaeological
si es such as Sie a de A apue ca, limi ing hei s udy and
equi ing consolida ion ea men s o enable examina ion
and conse a ion. Sie a de A apue ca (Bu gos, Spain) is
a limes one ka s complex wi h many ca i ies in which
a chaeological ieldwo k has been sys ema ically ca ied ou
since 1978 [2]. The a chaeological si e has p o ided c ucial
da a on human e olu ion in Eu asia om 1.2 My o he
end o he Middle Pleis ocene [4]. The e o e, i was included
in he UNESCO’s Wo ld He i age lis in 2000. Fieldwo k
ex ended h oughou he ca e sys em and a ound he ange,
including open-ai and ock shel e si es, has inc eased he
ime pe iod up o Holocene occupa ions [6].
The che samples included in his s udy come om G an
Dolina and Gale ía (Figu e 1a), wo o he ca e si es loca ed
in he T inche a del Fe oca il. The s one ools eco ded
a Gale ía and G an Dolina Ca es comp ise a ious aw
ma e ials such as sands one, qua zi e, and o he less well-
ep esen ed ma e ials, bu he majo i y a e che a i ac s,
pa icula ly Neogene che ha is usually highly al e ed. I is
o med a e silica p ecipi a ion in a hype saline en i onmen
ich in gypsum and ca bona es. I appea s in he Neogene
bo de o he Due o Ri e and belongs o he la e Miocene [10].
Almos all he Neogene che a i ac s om he A apue ca
si es ha e been whi ened and los hei o iginal lus e . They
also p esen isibly inc eased su ace po osi y, wi h an
aspec ha co esponds o he commonly desc ibed “whi e
pa ina” [11]. The al e a ion, howe e , does no concen a e on
he su ace; in ac , i is mo e p onounced in he inne pa ,
whe e usually he che becomes powde [14]. In some cases,
his issue impedes he eco e y o in ac a i ac s om he
si e, as hey o en b eak du ing he exca a ion wo ks and, on
many occasions, equi e consolida ion be o e being li ed o
subsequen ly handled (Figu e 1b-d).
Up o now, he che a i ac s o he A apue ca si es ha e
p edominan ly been consolida ed wi h he ac ylic esin
Pa aloid B72 and, occasionally, wi h e hyl silica e-based
p oduc s [14].
Figu e 1. Che samples collec ed om Sie a de A apue ca (Bu gos, Spain) a chaeological si e: a) Uppe pa o G an Dolina si e; b) P io consolida ion
wi h ac ylic esin Pa aloid B72 o an al e ed che a i ac ound in he TD10.2 uni ; c) Li ing o he ea ed a i ac ; d) Che s one ool a e conse a ion
ea men s.
a
bcd
A. Zo noza-Inda , P. Lopez-A ce, L. López-Polín
22 CONSERVAR PATRIMÓNIO 36 (2021)
A chaeological che a i ac s om A apue ca si es (Bu gos, Spain)
The aim o his esea ch is o cha ac e ize che
samples collec ed om he a chaeological A apue ca si e
o de e mine hei composi ion, ex u e and conse a ion
s a e, as well as he causes o hei decay in o de o selec he
mos compa ible consolida ion ea men s. In addi ion, we
assessed he e icacy o he mos widely-used consolida ion
ea men s by compa ing changes on he aes he ic and
physical p ope ies o he ea ed subs a es wi h hose
p oduced by wo no el consolida ion p oduc s based on
SiO2 and Ca(OH)2 nanopa icles. These p oduc s a e s ill
no widely used by conse a o s o conse a ion pu poses
and un epo ed o a chaeological p ehis o ic s one ool
p ese a ion hus a .
Ma e ials and me hods
Che samples
In he A apue ca a chaeological si e, he che is di ided
in o wo pe ological g oups based on i s o igin and
geological pe iod o o ma ion, i.e., C e aceous and
Neogene [10, 16]. Neogene che comes om La e Miocene
o ma ions and is ound as la ge blocks ou c opping in
ma ls and ma ly limes one, and was o med due o silica
p ecipi a ion in a hype saline en i onmen ich in gypsum
and ca bona es [10]. P e ious s udies ha e de e mined ha
his ype o che is composed o qua z and mogani e; i
also con ains a ce ain amoun o gypsum, calci e ( illing
some po es), and occasional impu i ies. Mic oscopically i
appea s highly he e ogeneous and pa icula ly po ous in
c ys alline zones [17].
Six che samples classi ied as ha ing di e en deg ees o
decay based on isual inspec ion we e selec ed o de e mine
hei composi ion, ex u e and s a e o conse a ion (Table
1). The causes o hei decay we e also s udied wi h he
pu pose o being able o selec and e alua e he necessa y
conse a ion ea men s and he mos sui able consolida ing
p oduc s o p ese ing he samples. Fou samples o che
li hic emains came om he Middle Pleis ocene uni s o
he si e. Two o hem (samples SX3 and SX9) we e collec ed
om uni GIII o Gale ía si e, da ed a a ound 300 ky [18]
and ano he wo (samples SX1 and SX17) we e collec ed om
he TD10.2 uni in he uppe pa o G an Dolina and da ed
a a ound 400 ky [10, 20]. Two u he , esh che samples,
we e collec ed om he su ounding ou c ops in he Sie a
de A apue ca (samples SX18 and SX19) wi h he aim o
compa ing hese wi h he decayed samples collec ed om
he a chaeological si es (Figu e 2). The soil emains ha
co e ed he samples om he dig we e ca e ully emo ed
om hei su aces wi h a b ush, in o de o ca y ou he
composi ional and ex u al analyses o he clean che s.
S udy o consolida ion ea men s
Six een che samples om Middle Pleis ocene uni s we e
Nomencla u e Nomencla u e on si e
Yea Le el Squa e Nº
Middle Pleis ocene
li hic emains
SX1 2008 TD10 M18 341
SX3 2004 GIII N03 71
SX9 2004 GIII N03 70
SX17 2011 TD10 L13 66
F esh che samples
collec ed om he
su ounding ou c ops
SX18
SX19
Table 1. S udied che samples om A apue ca a chaeological si e.
Figu e 2. S udied che samples: a) Sample SX17; b) Sample SX9; c) Sample SX3; d) Sample SX1, om he a chaeological si e o A apue ca; e) Sample SX19,
and ) Sample SX18 om he su ounding ou c ops.
a c b
e d
23 CONSERVAR PATRIMÓNIO 36 (2021)
collec ed in wo di e en si es o e alua e he di e en
consolida ing p oduc s a e hei ea men . Six samples
we e selec ed om he TD10.2 uni in he uppe pa o G an
Dolina and en samples we e collec ed om uni GIII a he
Gale ía si e. The samples we e la ge enough o be analyzed
using a ious analy ical echniques and es me hods
(Table 2). The 16 selec ed samples ( ou con ol samples and 12
samples o be ea ed, h ee samples o each consolida ing
p oduc ) ini ially displayed a simila deg ada ion s a e, i.e.
milky whi e in colo , loss o densi y and mass, supe icial
decohesion, la ge oughness, iable su ace and loss o
ex e nal a eas (apa om samples SX2 and SX8 which
p ese ed some pa s o he mos supe icial a ea). As
explained abo e, he soil co e ing he samples was b ushed
o o enable hei cha ac e iza ion and u he applica ion
o he consolida ing p oduc s.
As i was desc ibed in a p e ious wo k by Zo noza-
Inda e al. [21], ou ypes o consolida ing p oduc s
we e applied o consolida e che a i ac s (Table 2). The
i s one comp ises he mos widely-used con en ional
alkoxysilane consolidan (e hyl silica e: Tego akon V100,
E onik Indus ies AG). This p oduc was chosen because
i is highly compa ible wi h siliceous subs a es and can
o m chemical bonds wi h subs a es con aining hyd oxyl
g oups du ing he sol-gel p ocess [22]. The second p oduc
was a colloidal dispe sion o silica nanopa icles in wa e
(Nano Es el, C.T.S.) wi h a pa icle size o 10-20 nm and a
concen a ion o 150 g/L. This p oduc was chosen because
i is a no el p oduc and is also expec ed o be chemically
compa ible wi h siliceous subs a es due o he o ma ion
o a silica gel wi h silanol g oups [23].
The hi d p oduc was an ac ylic esin, he mos widely-
used by conse a o s (Pa aloid B72 by Dow Chemical), in a
concen a ion o 5 % in xylene. The choice o sol en is based
on i s ola ili y. When Pa aloid is used as a consolidan , a
low ola ile sol en is used o allow maximum pene a ion
o he p oduc (conse a o s use o apply ace one as a sol en
when he p oduc is used as an adhesi e because he apid
e apo a ion a e o he ace one dec eases he pene a ion
o he p oduc in he po ous ne wo k emaining only on he
su ace). Al hough Pa aloid is he mos used consolidan ,
silica e-based p oduc s wi h a lesse pene a ion dep h han
e hyl has been epo ed [24].
Finally, a mix u e o wo ino ganic p oduc s based
on colloidal dispe sions o nanopa icles was used ( he
a o emen ioned Nano Es el, and Nano es o e C.T.S., i.e.
Ca(OH)2 colloidal dispe sion in isop opyl alcohol wi h a
pa icle size o ≤ 100 nm and a concen a ion o 5 g/L), in a
a io o 1:1.
The p oduc s we e applied o ep oduce he applica ion
me hod used nowadays by mos es o e s, which usually
ollow he ecommenda ions s a ed by he manu ac u e s.
The applica ion was pe o med h ough a capilla y ube
and deposi ed d op-by-d op ( he mos equen ly used
applica ion me hod in conse a ion o a chaeological
a i ac s) on o he su ace o he samples. Then, he samples
we e exposed o a humid en i onmen (19 ± 1 oC empe a u e
(T) and 93 ± 3 % ela i e humidi y (RH)) o one mon h,
e en hough i should be no ed ha he ime sugges ed by
he manu ac u e (2-4 weeks) migh no be ime enough
o comple e he polyme iza ion p ocess. This high RH
was selec ed because he ca bona ion a e o Ca(OH)2
nanopa icles is as e unde highe RH [25]. In addi ion,
new silica nanopa icles can be used in condi ions whe e
e hyl silica e o ac ylic esin a e no app op ia e, such as in
he p esence o high le els o humidi y, ee wa e o we
Table 2. Che samples and applied consolida ing p oduc s by d ipping.
Nomencla u e Nomencla u e on si e Applied consolida ing p oduc
Yea Le el Squa e Nº Consolida ing p oduc Comme cial p oduc Applied amoun
o p oduc (g)
MC SX1 2008 TD10 J19 85
Con ol samples
MC SX2 2004 GIII N03 71
MC SX3 2004 GIII N03 71
MC SX4 2011 TD10 K14 151
SX1 2008 TD10 M18 341 Nano SiO2Nano Es el 1.09
SX2 2008 TD10 J19 85 2.29
SX3 2004 GIII N03 71 1.2
SX4 2004 GIII N03 71 E hyl silica e Tego akon V100 2.23
SX6 2004 GIII N03 71 0.59
SX7 2004 GIII N03 71 1.41
SX8 1998 TD10 N14 34 Ac ylic esin Pa aloid B72 2.11
SX9 2004 GIII N03 70 1.11
SX13 1998 TD10 N14 34 1.53
SX10 2004 GIII N03 70 Nano SiO2 + Ca(OH)2Nano Es el +
Nano es o e
1.54
SX11 2004 GIII N03 70 1.33
SX12 2004 GIII N03 70 1.22
A. Zo noza-Inda , P. Lopez-A ce, L. López-Polín
24 CONSERVAR PATRIMÓNIO 36 (2021)
su aces. No e ha mois u e is common in a chaeological
exca a ed objec s, which can gene a e compa ibili y
p oblems wi h conse a ion p oduc s. The empo a y
hyd ophobici y o e hyl silica es, al eady in es iga ed by
o he au ho s, can p eclude u u e ea men s, as he
consolida ion ea men is usually ollowed by cleaning
o he samples. In his deepe cleaning p ocedu e, hyd ic
sol en s a e used, bu , he cleaning is no possible i he e is a
hyd ophobic laye . In addi ion, i a olume ic ein eg a ion
is made and he su ace is hyd ophobic, he adhesion o he
ein eg a ion s uccos is hinde . Also, he hyd ophobici y
o some consolidan s p eclude desalina ion ea men s
( e y common in bu ied a chaeological pieces). Al hough
he concep o e e sibili y has been widely s udied and
discussed, he concep o e ea abili y is less s udied.
Resea ch is usually ocused on he applica ion o hese
ea men s, especially consolida ion p oduc s o eshly
exca a ed o de e io a ed ma e ials bu no o samples ha
ha e been al eady ea ed wi h o he p oduc s. The e o e
and despi e being one o he mos impo an c i e ia in
he selec ion o conse a ion p oduc s and ea men s,
e ea abili y is less conside ed in conse a ion s udies.
The ime o his hyd ophobic beha io a ies acco ding
o he au ho s and he esea ch, as well as wi h comme cial
p oduc s applied and subs a es ea ed. The hyd ophobici y
has been obse ed un il 28 days o cu ing [26], i e weeks
[27], h ee weeks [28], one mon h [29], wo mon hs [30] and
se e al mon hs [22, 31].
En i onmen al da a logge s, ibu ons model DS1923-F5,
we e in oduced in o he con aine and also placed in he
labo a o y o egis e T and RH du ing he es , using he
so wa e OneWi eViewe e sion 3.04. Fu he de ails on
he use o hese consolida ing p oduc s, applica ion me hod
and en i onmen al condi ions a e desc ibed in Zo noza-
Inda e al. [21].
Analy ical echniques and es me hods
Che cha ac e iza ion
The decay and conse a ion s a e o he samples was s udied
ollowing he p o ocol and e ms es ablished by Fon e al.
[15] based on mac o- isual inspec ion wi h he naked eye.
In addi ion, X- ay di ac ion (XRD) was used o de e mine
he main mine alogical phases and deg ee o c ys allini y
o he samples. A Phillips PW-1710 di ac ome e was used
wi h CuKα adia ion o s udy he o al powde ac ion
o samples. The measu emen s we e conduc ed by s ep
scanning 2θ om 2 o and 68 o, scan s ep size 0.02 o, scanning
a e 2 o/min, wi h a con inuous mode and beam in ensi y
o 40 kV and 40 mA. Th ee che samples (SX3, SX17 and
SX18) we e analyzed wi h highe p ecision o dis inguish
he di e en silica polymo phs by means o a mul i-pu pose
PANaly ical X´Pe MPD wi h CuKα adia ion. Analysis
condi ions we e 2θ be ween 2 o and 90 o, scan s ep size 0.02 o,
coun ime o 3 seconds pe s ep, wi h con inuous mode and
beam in ensi y o 45 kV and 40 mA. Fu he mo e, sample
SX18 was p ese ed and analyzed, wi hou g inding, using
mic o-di ac ion analyses o ob ain se e al di ac og am
pa e ns on a ious spo s o in e es . The mine alogical
phases we e iden i ied by compa ing he sample wi h he
Join Commi ee on Powde Di ac ion (JCPDS) da abase
and B uke AXS Di acPlus EVA so wa e.
Ion ch oma og aphy (IC) analyses we e pe o med o
iden i y soluble sal s in all he samples, i.e. ype and quan i y
o some anions (Cl−, NO3− and SO42−). Soil samples collec ed
om he same dig a eas as he che samples we e also
analyzed o asce ain whe he o no he p esence o sal s.
App oxima ely 0.1 g o sample was dissol ed in 10 ml o
Milli-Q ul apu e wa e and placed o 45 min in an ul asonic
ba h a oom empe a u e. A e wa d i was cen i uged
o 5 min a 3500 pm and 3400 c cen i ugal o ce. The
soluble sal s in he ex ac ed sample we e quan i ied using a
Me ohm 761 Compac IC ion ch oma og aph.
The su ace mo phology and ex u e o he specimens
we e examined by means o en i onmen al elec on scanning
mic oscopy (ESEM) using an Inspec FEI mic oscope
coupled wi h ene gy dispe si e X- ay spec oscopy (EDS)
(model 7509 Ox o d Ins umen Analy ical, UK).
Op ical su ace oughness (OSR) analyses we e also
pe o med on he su ace o samples SX18 and SX19 ( he
o he samples we e oo small o ake hese measu emen s
on). This was ca ied ou o e alua e changes in he su ace
oughness caused by decay p ocesses. The equipmen
used was a con ac - ee su ace p o ilome e (whi e ligh ),
TRACEiT, Innowep GmbH. The OSR analyses included he
gene a ion o 3D- opog aphy maps (25 mm2) using Gyddion
2.44 so wa e displaying he a e age oughness pa ame e s
acco ding o ISO 4287 (1998) s anda ds [33], i.e., Ra
(a i hme ic mean o he absolu e alues o p o ile de ia ions
om he mean line) and Rz (sum o he e ical dis ances
be ween he i e highes peaks and he i e deepes alleys
wi hin he sampling leng h). The cu o (λc) used o he
calcula ions was 0.80 mm.
Consolida ion
The six een specimens we e also analyzed using a ious
non-des uc i e echniques and es me hods bo h be o e
applica ion o he consolida ing p oduc s and one mon h
la e .
The su ace mo phology, ex u e o he specimens, and
he dis ibu ion and mo phology o consolida ing p oduc s
was examined by ESEM-EDS.
A peeling es was ca ied ou on he su ace o he
samples o assess he de achmen deg ee o he ma e ial
using anspa en double-sided adhesion ape (Tesa), wi h
1.5 cm wide × 5 cm long, on 1 zone pe sample ( en sequences)
and 90 seconds pe each sequence. This me hod is commonly
used o e alua ing he consolida ion e ec o he p oduc s
on s one su aces by de e mining he de ached ma e ial
a e applying and emo ing p essu e sensi i e ape o e
he su ace [34].
A chaeological che a i ac s om A apue ca si es (Bu gos, Spain)
25 CONSERVAR PATRIMÓNIO 36 (2021)
Spec opho ome y was pe o med o de e mine he
colo pa ame e s, wi h a spec opho ome e MINOLTA
CM-700d using he CieLab colo space; he measu ing a ea
was 1-3 mm. Th ee measu emen s we e conduc ed o each
sample, he s anda d illuminan was D65 and he obse e
angle, 10 o. The measu ed pa ame e s we e L*, which accoun s
o luminosi y, a* and b* coo dina es (a* being he ed-g een
pa ame e and b* he blue-yellow), o al ch ome di e ence
ΔC* ( om he o mula ΔC* = (Δa*)2 + (Δb*)2)1/2), and o al
colo di e ence ΔE* ( om he o mula ΔE* = ((ΔL*)2 + (Δa*)2
+ (Δb*)2)1/2). The whi e (WI) and yellow (YI) indices we e
measu ed acco ding o ASTM E313-73 [35] and b igh ness
was measu ed acco ding o ISO 2470-2 [36].
Resul s and discussion
Cha ac e iza ion o che samples
Mac oscopic examina ion
The main esul s om he mac oscopic examina ion a e
shown in Table 3. All he wea he ed samples om he
a cheological si es displayed a milky-whi e colo and los he
cha ac e is ic densely packed cohesion o che . No issu es
o ac u es we e obse ed wi h he naked eye in any o he
samples. Howe e , all o hem showed a coa se su ace wi h
di e en deg ees o decohesion (Figu e 2a-d). Sample SX17
(Figu e 2a) was he mos damaged che . Pa o his sample
was b oken down in o a whi e powde and he es was e y
dus y, iable and disagg ega ed on he su ace. Sample
SX9 (Figu e 2b) displayed a ce ain deg ee o compac ed
s uc u e, sligh ly highe han he p e ious sample. I also
had a dus y, iable and disagg ega ed su ace ha powde ed
o he ouch. In spi e o some los ma e ial, samples SX3 and
SX1 (Figu e 2c-d) seemed o be be e p ese ed compa ed
o he o he samples. These we e mo e compac ed and
did no p esen he same deg ee o disagg ega ion as he
p e ious samples, e en hough hey also had coa se, g ainy
and qui e dus y su aces. Among he che samples om
he ou c ops su ounding he a chaeological si es, sample
SX19 (Figu e 2a) was muddy-whi e in colo wi h a coa se
bu compac ed su ace, simila o samples SX1 and SX3.
Two di e en zones could be dis inguished on he su ace
o his sample, a mo e c ys alline, compac ed and smoo he
co e zone, and ano he whi e , coa se and dus ie ex e nal
zone ha appea ed mo e wea he ed. Sample SX18, also
om he su ounding ou c ops, was g ayish-b own in
colo wi h some ace ed co e a eas ha we e ine g ained
and c ys alline (Figu e 2 ). Only his la e zone o his
pa icula sample displayed he cha ac e is ic cu ing
edge mo phology caused by he dis inc i e conchoidal
ac u e o he che . This co e zone was su ounded by a
1 mm- hick c us , g ayish-whi e in colo and ea hy bu
wi h a compac ed appea ance. This was ci cled by ano he
5 mm- hick, whi e ex e nal c us ha in spi e o i s compac ed
s uc u e displayed a simila aspec o he mo e wea he ed
samples p e iously desc ibed (milky-whi e in colo , ough,
dus y and wi h a disagg ega ed su ace).
X- ay di ac ion (XRD)
All he XRD esul s ob ained om he o al powde samples
showed he p esence o qua z (SiO2) and mogani e (SiO2
polymo ph), wi h he excep ion o SX9 and SX17 which we e
solely composed o qua z and calci e (CaCO3); SX17 had
a la ge amoun o calci e. These esul s a e in ag eemen
wi h hose ob ained by o he au ho s o simila ma e ials
[17, 37]. Sample SX19 had mo e mogani e in he whi e
ex e nal zone compa ed o he mo e c ys alline co e zone.
The amoun o mogani e was e en highe in sample SX3,
which also displayed some calci e, ollowed by sample SX18
(Figu e 3a). The ou di ac og am pa e ns ob ained in
di e en spo s on his ung ound sample indica e ce ain
mine alogical di e ences (Figu e 3b). The ex e nal zone
(su ounding c us ; c us 1) was mainly composed o qua z
and calci e wi h a lowe p opo ion o dolomi e, and had
poo ly-de ined b oad peaks indica ing less c ys allini y. The
mos ex e nal whi e c us (c us 2) showed only qua z and
e y well-de ined mogani e peaks. The qua z peak a 41 o
2θ only appea ed well-de ined in he c ys alline co e zones
o he sample (Che 1; Figu e 3b). As inside he same nodule
o qua z le el ex u es and impu i ies can change, ha ’s
he main di e ence be ween he ace ed and colo ed a eas
in he c ys alline co e zone o he sample [38]. This is also
he main di e ence be ween he ace ed and colo ed a eas
in he c ys alline co e zone o his sample, since changes in
ex u e and impu i ies can occu inside he same nodule o
qua z le el [38].
The che samples om he a chaeological si e and he
mos wea he ed samples om he su ounding ou c ops
(wi h a o ally disagg ega ed su ace), i.e., samples SX17,
SX9 and he mos ex e nal c us o sample SX18, displayed
qua z and calci e mine als. The less-wea he ed samples,
Nomencla u e Mac oscopic examina ion
Middle
Pleis ocene
li hic
emains
SX1 Be e p ese ed. Mo e compac ed, wi hou
disagg ega ion bu wi h coa se, g ainy and
qui e dus y su aces.
SX3
SX9
Ce ain deg ee o compac ed s uc u e bu ,
dus y, iable and disagg ega ed su ace
ha powde ed o he ouch.
SX17
Mos damaged. B oken down in o a
whi e powde , e y dus y, iable and
disagg ega ed on he su ace.
F esh che
samples
SX18
G ayish-b own in colo wi h some ace ed
co e a eas ha we e ine g ained and
c ys alline.
SX19
Muddy-whi e in colo wi h a coa se bu
compac ed su ace. Two di e en zones: a
mo e c ys alline, compac ed and smoo he
co e zone, and ano he whi e , coa se and
dus ie ex e nal zone ha appea ed mo e
wea he ed.
Table 3. Mac oscopic examina ion o a chaeological che samples.
A. Zo noza-Inda , P. Lopez-A ce, L. López-Polín
26 CONSERVAR PATRIMÓNIO 36 (2021)
wi h coa se, g ainy bu mo e compac ed su aces (samples
SX1, SX3, SX19 and middle c us o sample SX18), con ained
qua z, mogani e and small amoun s o calci e. Finally, he
bes p ese ed c ys alline co es o samples SX18 and SX19
had only qua z.
High alkalini y, sul a es and e ic ion ac i i y play a
ce ain ole in he p ecipi a ion o mogani e [38]. In he
esea ch wo k on Mogan ocks om G an Cana ia, Spain,
ca ied ou by Ga cía-Guinea e al. [39], i was ound ha
hei co e a ea and edges (mo e po ous, whi e and wi h
addi ional ions) esul ed in a di e en ca hodoluminescence
spec um. This was in e p e ed as la e hyd o he mal
wea he ing mechanisms wi h alkaline ions, me als and
ola iles o o m mogani e. In silica wea he ing, mogani e
ep esen s an in e media e posi ion be ween opaline phases
and qua z [38]. I is conside ed a me as able phase which can
be ans o med in o qua z i he e is enough ime o he e
a e changes in he su ounding en i onmen al condi ions
[40]. The abundance o mogani e in a id en i onmen s has
been pa ially explained by he lack o wa e o media ing
he dissolu ion o his mine al and he simul aneous
p ecipi a ion o qua z, as be ween 10 % and 80 % o he silica
p esen in di e en a ie ies o ine-g ained qua z is in
ac mogani e [41]. In his case, he quan i y o mogani e is
a key indica o in he decay o che samples. The c ys alline
co e zone o sample SX18 om he ou c ops, which only has
qua z, is in a good s a e o p ese a ion. The che samples
om he a cheological si e and he ou e c us o sample
SX18 (wi h mix u es o qua z-mogani e) a e wea he ed,
wi h coa se, po ous and disagg ega ed su aces. In qua z-
mogani e mix u es, as wea he ing may occu , as mogani e
is mo e soluble han qua z. This means ha hose pa s o
he che con aining mogani e could be mo e wea he ed
and mo e po ous, a o ing luid pene a ion leading o
disagg ega ion p ocesses. In he esea ch conduc ed by
Na azo e al. [17], poo ly-p ese ed Neogene che , and
massi e, well-p ese ed C e aceous che samples wi h low
po osi y, bo h om ou c ops close o he A apue ca moun ain
ange, we e compa ed. They also ound ha mogani e played
a signi ican ole in che decay and p ese a ion s a e,
since he quan i y o his mine al was he main di e ence
be ween he wo ypes o che . Inc eased amoun s o calci e
and dec eased mogani e in he samples, ela ing o a g ea e
deg ee o decay and wea he ing, may be due o he ac ha
he a eas o iginally comp ising mogani e could ha e been
wea he ed o dissol ed. This a o s luid pene a ion and
po e illing by ex e nal compounds [39], in his case by calci e
since hese che s we e wi hin limes ones ock se lemen s.
The absence o mogani e in he mos wea he ed che
samples could be in line wi h he da a p o ided by Heaney
& Pos [41] and Rodge s & C essey [40], who epo ha
mogani e does no appea in wea he ed o e oded che s,
since i comple ely disappea s due o dissolu ion p ocesses.
Ion ch oma og aphy (IC)
Ion ch oma og aphy da a indica e negligible amoun s o
soluble sal s (chlo ides, ni a es and sul a es), wi h o al
weigh pe cen ages o sal s below 0.08 % in all samples
as i was desc ibed in Zo noza-Inda e al. [21]. The soil
samples collec ed om he same dig a eas whe e he che
samples we e bu ied also con ain insigni ican amoun s
o sal s. The e o e, he decay o he che samples by sal
c ys alliza ion p ocesses is discoun ed.
Op ical su ace oughness (OSR)
The su ace oughness analysis esul s a e shown in Table 4.
Figu e 3. X- ay di ac ion (XRD) pa e ns o he a chaeological che
samples: a) XRD ob ained om he o al powde samples; b) Di ac og ams
om mic o XRD analysis (no powde ed samples) ob ained in SX18 sample,
in he ex e nal (c us ) and in he co e zones (che ). Q: qua z; Mog:
mogani e; C: calci e; D: dolomi e.
a
b
Sample A ea Ra (µm) Rz (µm)
SX18 Smoo h 2.57 ± 0.40 9.35 ± 1.37
C us 7.43 ± 0.34 40.82 ± 1.84
SX19 Smoo h 3.67 ± 0.29 17.52 ± 1.12
Wea he ed 10.30 ± 0.42 41.62 ± 1.94
Table 4. Op ical su ace oughness (OSR) pa ame e s (Ra and Rz) o esh
che samples SX18 and SX19, measu ed on he ex e nal c us , wea he ed
su aces and smoo h a eas.
A chaeological che a i ac s om A apue ca si es (Bu gos, Spain)
27 CONSERVAR PATRIMÓNIO 36 (2021)
The mic o-de ailed su ace images can be seen in Figu e 4,
and 3D OSR maps a e p esen ed in Figu e 5.
By compa ing he esul s ob ained on he smoo h,
c ys alline co e zones and less wea he ed pa s ( ha a e
mo e simila o esh che ) o he wo s udied samples
(SX18 and SX19), i can be seen ha he Ra oughness
alues o sample SX19 a e 43 % highe han o sample SX18
(3.67 ± 0.29 µm s. 2.57 ± 0.40 µm, espec i ely). The same
occu s wi h he Rz alues ha a e 87 % highe in sample
SX19 (17.52 ± 1.12 µm s. 9.35 ± 1. 37 µm). These esul s show
ha sample SX19 is much coa se han sample SX18 due o
su ace deg ada ion p ocesses, as was also obse ed in he
mac oscopic s udy. The a e age su ace oughness alues a e
g ea e in bo h he smoo he and be e -p ese ed a eas and
ac oss he en i e su ace o sample SX19, which is deno ed by
he longe dis ances be ween he highes and deepes pa s
o he measu emen a eas indica ed by he Rz pa ame e .
In he coa se and decayed a eas, he ough and dus y
ex e nal zone o sample SX19 and he ex e nal c us o SX18
(c us 1, which acco ding o XRD comp ises qua z and
calci e), oughness alues a e simila in he wo samples,
al hough sligh ly highe in sample SX19 (7.43 ± 0.34 µm s.
10.30 ± 0.42 µm in he Ra pa ame e and 40.82 ± 1.84 µm s.
41.62 ± 1.94 µm in he Rz pa ame e espec i ely).
The mic o-de ailed images ob ained wi h he p o ilome e
(Figu e 4) and he su ace oughness 3D heigh maps
Figu e 4. Mic o-de ailed images ob ained by op ical su ace oughness (OSR) measu emen s: a) E en a ea o sample SX18; b) Ex e nal c us o he sample
SX18; c) Coa se su ace ex u e o sample SX19.
Figu e 5. Su ace oughness 3D heigh maps ob ained unde op ical su ace oughness (OSR) on he di e en su ace a eas o che SX18 and SX19
samples: a) E en a ea o sample SX18; b) Ex e nal c us o he sample SX18; c) E en a ea o sample SX19; d) Coa se su ace o sample SX19.
a b c
b
a
c d
A. Zo noza-Inda , P. Lopez-A ce, L. López-Polín
28 CONSERVAR PATRIMÓNIO 36 (2021)
(Figu e 5) show he su ace di e ences on he ex u e
mo phology, and hence he su ace oughness con as
among se e al zones o bo h samples. The image o an
e en a ea o sample SX18 shows a smoo h, compac ed and
homogeneous su ace (Figu e 4a and Figu e 5a), whe eas
he image o sample SX19 e eals a whi e colo and dus ie ,
poo ly-compac ed su ace, whe e mine al g ains a e clea ly
obse ed, as well as discon inuous a eas wi h po es (Figu e
4c and Figu e 5c-d). In he mos decayed a eas, some u he
di e ences can be seen (Figu e 5b-d). The ansi ion om
he smoo h a ea owa ds he ex e nal ough zone o sample
SX19 can be obse ed as a p og essi e loss o homogenei y
and compac ion o he su ace, showing up as a mo e
whi e and po ous, disagg ega ed g ainy zone whe e loss o
ma e ial is obse ed. In sample SX18, he image shows he
p e ious s ep in he o al decay p ocess obse ed in sample
SX19. The colo is s ill da ke han he su ace colo ing
o sample SX19, al hough whi e a eas no de ec ed in he
smoo h zone can be obse ed. The su ace o SX18 sample
main ains i s con inui y and homogenei y, bu c acks and
issu es appea and, e en ually, i decay p ocesses con inue,
he e could be loss o ma e ial and disagg ega ion o he
su ace, in a simila way o ha obse ed in sample SX19.
En i onmen al SEM-EDS
Sample SX3 om he a chaeological si e exhibi s silica wi h
adial- ib ous ex u es in some a eas and nodula ex u es
in o he s (Figu e 6). E en hough sample SX17 is mo e
homogenous, he ib ous ex u e is less igidly o ien ed
(Figu e 6d).
The ex e nal pa o sample SX18, om he ou c op,
shows signs o dissolu ion, e ac ion c acks and has
a highe calcium con en (Figu e 7a). A di e en zone
(co esponding o he whi ish c us ) displays a simila
ex u e o he c ys alline co e zone. Howe e , in his case i
is wea he ed due o dissolu ion- ec ys alliza ion p ocesses
(Figu e 7b). In he c ys alline co e zone, a c yp o-c ys alline,
ai ly ib ous ex u e can be seen (Figu e 7c), oge he wi h
some a eas con aining po es and issu es om 50 o 100 µm
in size, almos comple ely cemen ed by mic o-c ys alline
qua z c ys als (Figu e 7d). These po e and issu ed a eas
migh co espond o mogani e, leading o a ce ain deg ee
o mic o-po osi y.
These esul s a e in line wi h hose ob ained by XRD, whe e
di e ences be ween he wo c us s we e dis inguished ( he
ou e c us had a highe deg ee o al e a ion and comp ised
qua z and calci e, while he o he c us was composed o
calci e and mogani e). Va iabili y in mogani e con en has
been linked o mac oscopic colo and ex u e a ia ions
wi hin a sample, indica ing ha a iable mogani e con en
may be linked o changing en i onmen al o deposi ional
condi ions [42]. The ou e zone o sample SX19 p esen s
c ys als wi h adial- ib ous mo phologies (which could
be mogani e) oge he wi h nodules o agglome a ed
Figu e 6. En i onmen al SEM (ESEM) images om he a chaeological si e che samples: a) Sample SX3; b) De ail o adial- ib ous ex u e a ea in o me
sample; c) De ail o nodula ex u es in he same sample; d) De ail o diso ien ed ib ous ex u e in sample SX17.
a b
c d
A chaeological che a i ac s om A apue ca si es (Bu gos, Spain)
35 CONSERVAR PATRIMÓNIO 36 (2021)
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RECEIVED: 2019.10.8
REVISED: 2020.4.1
ACCEPTED: 2020.4.9
ONLINE: 2020.6.29
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A. Zo noza-Inda , P. Lopez-A ce, L. López-Polín
