Sci­en­tists study ways to pre­serve world her­itage sites

Small arms fire has huge ef­fect on an­cient struc­tures.

Austin American-Statesman - - WORLD - By Melissa Healy Los An­ge­les Times

An­cient her­itage sites caught in the cross­fire of war are, in many ways, lit­tle dif­fer­ent from civil­ian pop­u­la­tions trapped in the midst of armed con­flict: Even when they con­tinue to stand, they are crum­bling in­side.

A new study set out to re-cre­ate the im­pact of small arms fire on stone col­umns and struc­tures that have en­dured thou­sands of years of sun, wind and rain. When struck by small arms fire, it found, these an­cient ar­ti­facts show lit­tle sign of out­ward dam­age.

But the im­pact of a .22-cal­iber bul­let cre­ates a net­work of tiny cap­il­lar­ies that spreads be­neath the stony sur­face of, say, a col­umn or its cap­i­tal. As wa­ter or environmental tox­ins seep into those newly opened ves­sels, the re­sult is likely to be the rapid degra­da­tion of ir­re­place­able an­tiq­ui­ties.

The new study was pub­lished in the jour­nal Royal So­ci­ety Open Science.

Com­pared with the firearms wielded by armies, mili­tias and in­sur­rec­tion­ists across the world’s hot spots, the .22-cal­iber ri­fle used by the re­searchers is prac­ti­cally a spit­ball to a struc­ture that has baked in the sun and been pelted by rain, wind and snow for mil­len­ni­ums.

But the re­searchers had to start some­where, they wrote. De­spite re­ports that world her­itage sites have been caught up in con­flicts in Iraq, Afghanistan, Syria, Libya and Ye­men, the ef­fect that fly­ing bul­lets have on the in­tegrity of struc­tures built thou­sands of years ago has scarcely been stud­ied.

And when they used an AK-47 to study the im­pact of weapons fire on blocks of quar­ried stone, the re­searchers found they had lit­tle left to in­ves­ti­gate.

To gauge the im­pact of small-arms fire on the kinds of struc­tures found in ar­chae­o­log­i­cal sites across the Mid­dle East and Europe, the re­searchers got freshly quar­ried stone from the Huesca re­gion of north­east Spain.

This sand­stone - largely com­posed of quartz, gyp­sum, cal­cite and mus­covite - is pretty typ­i­cal of the kind of stone used in many of the Western world’s her­itage sites. Eons of ex­po­sure to the el­e­ments causes chem­i­cal changes in the stone that makes up many an­cient struc­tures, giv­ing them a hard­ened outer shell. To mimic that ef­fect, the re­searchers ap­plied to half of the test stones a preser­va­tive, called Wacker OH 100, that is some­times used by ar­chae­o­log­i­cal con­ser­va­tors to har­den the sur­face of del­i­cate or newly ex­posed stone struc­tures.

At a ri­fle range in Ox­ford­shire, Eng­land, the re­searchers took up po­si­tions 20 me­ters from their stony sub­jects and fired four .22-cal­iber lead bul­lets at each. They then car­ried the stones back to a lab and ei­ther sat them in a pud­dle of wa­ter or plunged them into a spe­cial cab­i­net that mim­ics the ex­treme tem­per­a­tures and con­di­tions of the arid and semi­arid Mid­dle East.

The ef­fects, seen un­der mi­cro­scopes, in X-ray im­ages and in to­mo­graphic scan­ners, “were far greater than ap­pre­ci­ated from a vis­ual in­spec­tion,” the au­thors wrote. Stone treated with the Wacker OH 100 preser­va­tive - and prob­a­bly an­cient build­ing ma­te­rial that has nat­u­rally de­vel­oped a tough outer crust - ap­pears to trans­mit the en­ergy of a bul­let to the area be­hind the im­pact.

Not only is the sur­face wound sub­ject to the in­dig­ni­ties of environmental ex­po­sure, but frac­ture net­works have formed be­neath, the au­thors wrote. As mois­ture fol­lows these paths, the re­sult could ac­cel­er­ate the stone’s de­te­ri­o­ra­tion.

Un­til re­cently, preser­va­tion­ists, ar­chae­ol­o­gists and clas­si­cal schol­ars thought the prin­ci­pal threats to the world’s cul­tural trea­sures were age, ex­po­sure to the el­e­ments and, oc­ca­sion­ally, a sur­feit of hu­man en­thu­si­asm for them. Now, these trea­sures are not only be­com­ing col­lat­eral dam­age in armed con­flicts with pow­er­ful weapons. At the hands of such groups as the Is­lamic State, ar­chi­tec­tural an­tiq­ui­ties have them­selves be­come the tar­get of at­tack.

“These tests are based on rel­a­tively small .22-cal­iber bul­let im­pacts with min­i­mal sur­face ma­te­rial loss,” the au­thors of the new study wrote. “The re­sults from this study, there­fore, beg the ques­tion; if such small im­pacts can al­ter the stone to this ex­tent, what are the longterm con­se­quences of larger im­pacts such as AK-47s?”

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