The authors gratefully acknowledge Ms. Christine Stefani for performing the XRPD measurements. Marian Schu&#776;ch and Rebekka Kuiter (State Academy of Art and Design Stuttgart) are acknowledged for the pictures of the tile (Fig. 7).

1. Sample Preparation
<ol>
	<li>Collection of material
	<ol>
		<li>Carefully pick a small amount (less than 1 mg) of sample 1 under a digital microscope using a scalpel and tweezers from settings of opaque blue-green cabochons on a historic clasp, belonging to the collection of the Rosgartenmuseum Konstanz (RMK-1964.79) (Figure 6).</li>
		<li>Carefully scratch a few mg of sample 2 with a scalpel from the surface of a glazed ceramic tile, dating at early modern times, manufactured in So...

<ol>
	<li>Bradley, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The interface between science and conservation, Occacional Paper 116. , (1997).</li><li>Dinnebier, R. E., Billinge, S. J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Powder Diffraction:Theory and Practice. , (2008).</li><li>Debye, P., Scherrer, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interferenzen+an+regellos+orientierten+Teilchen+im+Roentgenlicht.">Interferenzen an regellos orientierten Teilchen im Roentgenlicht.</a> Phys. Zeit. 17, 277-283 (1916).</li><li>Hull, A. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+New+Method+of+X-Ray+Crystal+Analysis.">A New Method of X-Ray Crystal Analysis.</a> Phys. Rev. 10 (6), 661-696 (1917).</li><li>Rietveld, H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+profile+refinement+method+for+nuclear+and+magnetic+structures.">A profile refinement method for nuclear and magnetic structures.</a> J. Appl. Cryst. 2, 65-71 (1969).</li><li>Oszlanyi, G., Suto, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ab+initio+structure+solution+by+charge+flipping.">Ab initio structure solution by charge flipping.</a> Acta Crystallogr. Sect. A. 60 (2), 134-141 (2004).</li><li>Newsam, J. M., Deem, M. W., Freeman, C. M., Prince, E., Stalick, J. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+Space+Methods+of+Structure+Solution+from+Powder+Diffraction+Data.">Direct Space Methods of Structure Solution from Powder Diffraction Data.</a> NIST Special Publication 864: Accuracy in Powder Diffraction II: Proceedings of the International Conference May 26-29, 1992. , 80-91 (1992).</li><li>Dinnebier, R. E., Run&#269;evski, T., Fischer, A., Eggert, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solid-State+Structure+of+a+Degradation+Product+Frequently+Observed+on+Historic+Metal+Objects.">Solid-State Structure of a Degradation Product Frequently Observed on Historic Metal Objects.</a> Inorg. Chem. 54 (6), 2638-2642 (2015).</li><li>Wahlberg, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystal+Structure+of+Thecotrichite,+an+Efflorescent+Salt+on+Calcareous+Objects+Stored+in+Wooden+Cabinets.">Crystal Structure of Thecotrichite, an Efflorescent Salt on Calcareous Objects Stored in Wooden Cabinets.</a> Cryst. Growth Des. 15 (6), 2795-2800 (2015).</li><li>Eggert, G., Fischer, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gef&#228;hrliche+Nachbarschaft:+Durch+Glas+induzierte+Metallkorrosion+an+Museums-Exponaten+-+Das+GIMME-Projekt.">Gef&#228;hrliche Nachbarschaft: Durch Glas induzierte Metallkorrosion an Museums-Exponaten - Das GIMME-Projekt.</a> Restauro. 1, 38-43 (2012).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> TOPAS (current version 5.0). , (2015).</li><li>Coelho, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Indexing+of+powder+diffraction+patterns+by+iterative+use+of+singular+value+decomposition.">Indexing of powder diffraction patterns by iterative use of singular value decomposition.</a> J. Appl. Crystallogr. 36 (1), 86-95 (2003).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> International Tables for Crystallography Volume A: Space-group symmetry. , (2006).</li><li>Pawley, G. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unit-cell+refinement+from+powder+diffraction+scans.">Unit-cell refinement from powder diffraction scans.</a> J. Appl. Crystallogr. 14, 357-361 (1981).</li><li>Cheary, R. W., Coelho, A. A., Cline, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fundamental+Parameters+Line+Profile+Fitting+in+Laboratory+Diffractometers.">Fundamental Parameters Line Profile Fitting in Laboratory Diffractometers.</a> J. Res. Natl. Inst. Stand. Technol. 109 (1), 1-25 (2004).</li><li>Karle, J., Hauptman, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+theory+of+phase+determination+for+the+four+types+of+non-centrosymmetric+space+groups+1P222,+2P22,+3P12,+3P22.">A theory of phase determination for the four types of non-centrosymmetric space groups 1P222, 2P22, 3P12, 3P22.</a> Acta Crystallogr. 9, 635-651 (1956).</li><li>Coelho, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Whole-profile+structure+solution+from+powder+diffraction+data+using+simulated+annealing.">Whole-profile structure solution from powder diffraction data using simulated annealing.</a> J. Appl. Crystallogr. 33 (3), 899-908 (2000).</li><li>Macrae, C. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mercury:+visualization+and+analysis+of+crystal+structures.">Mercury: visualization and analysis of crystal structures.</a> J. Appl. Crystallogr. 39 (3), 453-457 (2006).</li><li>Mittemeijer, E. J., Welzel, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Modern Diffraction Methods. , (2012).</li></ol>

The authors have nothing to disclose.

XRPD is a suitable technique for conservation research as it is non-destructive, fast and easy-to-use. XRPD data can be used in routine qualitative analysis, owing to the fact that the powder pattern is a fingerprint signature to the corresponding crystal structure. The biggest advantage of XRPD over other analytic techniques is the ability of performing simultaneous qualitative and quantitative analysis of crystalline constituents in mixtures by using the Rietveld refinement method5. Moreover, the presence of...

Conservation science applies scientific (often chemical) methods in the conservation of artifacts. This includes investigations of the production of artifacts (&#39;technical art history&#39;: How was it made at that time?) and their decay pathways as a prerequisite to develop proper conservation treatments. Oftentimes these studies deal with metal organic salts like carbonates, formates and acetates. Some of them have been deliberately manufactured using suitable compounds (e.g., vinegar), others derive from deterioration reactions with the atmosphere (carbon dioxide or carbonyl compounds from indoor air pollution)1. As a matter of fact, the crystal structures of many of these corrosion materials are still unknown. This is an unfortunate fact, since the knowledge of the geometrical structure helps conservation science to better understand production and decay reactions and to allow for full quantitative analysis in the case of mixtures.
Under the condition that the material of interest forms single crystals of sufficient size and quality, single crystal diffraction is the method of choice for the determination of the crystal structure. If these boundary conditions are not fulfilled, powder diffraction is the closest alternative. The biggest drawback of powder diffraction as compared to single crystal diffraction lies in the loss of the orientational information of the reciprocal d-vector d* (scattering vector). In other words, the intensity of a single diffraction spot is smeared over the surface of a sphere. This can be considered a projection of the three-dimensional diffraction (= reciprocal) space onto the one dimensional 2&#952;-axis of the powder pattern. As a consequence, scattering vectors of different direction but equal or similar length, overlap systematically or accidentally making it difficult or even impossible to separate these reflections2 (Figure 1). This is also the main reason why powder diffraction, despite its early invention just four years after the first single crystal experiment3,4, was mainly used for phase identification and quantification for more than half a century. Nevertheless, the information content of a powder pattern is huge as can be easily deduced from Figure 2. The real challenge, however, is to reveal as much information as possible in a routine way.
A crucial step towards this goal, without any doubt, was the idea from Hugo Rietveld in 19695 who invented a local optimization technique for crystal structure refinement from powder diffraction data. The method does not refine single intensities but the entire powder pattern against a model of increasing complexity, thus taking the peak overlap intrinsically into account. From that time on, scientists using powder diffraction techniques were no longer limited to data analysis by methods developed for single crystal investigation. Several years after the invention of the Rietveld method, the power of the powder diffraction method for ab-initio structure determinations was recognized. Nowadays, almost all branches of natural sciences and engineering use powder diffraction to determine more and more complex crystal structures, although the method can still not be regarded as routine. Within the last decade, a new generation of powder diffractometers in the laboratory was designed providing high resolution, high energy and high intensity. Better resolution immediately leads to better peak separation while higher energies fight absorption. The benefit of a better peak profile description based on fundamental physical parameters (Figure 3) are more accurate intensities of Bragg reflection allowing for more detailed structural investigations. With modern equipment and software even microstructural parameters like domain sizes and microstrain are routinely deduced from powder diffraction data.
All algorithms for crystal structure determination from powder diffraction data use single peak intensities, the entire powder pattern or a combination of both. The conventional single crystal reciprocal space techniques often fail due to an unfavorable ratio between available observations and structural parameters. This situation changed dramatically with the introduction of the &#34;charge flipping&#34; technique6 (Figure 4) and the development of global optimization methods in direct space, of which the simulated annealing technique7 (Figure 5) is the most prominent representative. In particular, the introduction of chemical knowledge into the structure determination process using rigid bodies or the known connectivity of molecular compounds concerning bond lengths and angles strongly reduces the number of necessary parameters. In other words, instead of three positional parameters for every single atom, only the external (and few internal) degrees of freedom of groups of atoms need to be determined. It is this reduction of structural complexity which makes the powder method a real alternative to single crystal analysis.
Two pioneering case studies of the authors8,9 proved that it is possible to solve complicated crystal structures of complex corrosion products using powder diffraction data. The superiority of the crystallographic studies compared to other approaches was demonstrated among others by the fact that in both cases the reported formulas had to be corrected after considering the solved crystal structures.
The occurrence of both materials under investigation in museums is related to their storage in wooden cabinets or exposed to other sources of carbonyl pollutants. The first material under investigation was sodium copper formate hydroxide oxide hydrate, Cu4Na4O(HCOO)8(OH)2&#8729;4H2O (sample 1), which forms on soda glass/copper alloy composite historic objects (e.g., enamels) in museum collections, exposed to formaldehyde and formic acid from wooden storage cabinets, adhesives, etc. This degradation phenomenon has recently been characterized as &#34;glass induced metal corrosion&#34;10. For the second case study, thecotrichite, Ca3(CH3COO)3Cl(NO3)2&#8729;6H2O (sample 2), was chosen. Thecotrichite is a frequently observed efflorescent salt forming needlelike crystallites on tiles and limestone museum objects, which are stored in oak cabinets and display cases. In this case, the wood acts as source for acetic acid which reacts with soluble chloride and nitrate salts from the artifact.
In the following part of the text, the individual steps of the structure determination process using powder diffraction data applied to corrosion products from conservation science are presented in detail.

<table border="0" cellpadding="0" cellspacing="0" width="573">
	<tbody>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Stadi-P&#160;</td>
			<td style="width:71px;">Stoe &#38; Cie GmbH</td>
			<td style="width:119px;"></td>
			<td style="width:167px;">Powder Diffractometer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Mythen 1-K (450 &#956;m)</td>
			<td style="width:71px;">Dectris Ltd.</td>
			<td style="width:119px;"></td>
			<td>Position Sensitive Detector</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Mark tube borosilicate glass No. 50, 0.5 mm diameter</td>
			<td style="width:71px;">Hilgenberg GmbH</td>
			<td align="right">4007605</td>
			<td>Low absorbing capillaries</td>
		</tr>
		<tr height="126">
			<td height="126" style="height:126px;width:216px;">Topas 5.0</td>
			<td style="width:71px;">Bruker AXS Advanced X-ray Solutions GmbH</td>
			<td style="width:119px;"></td>
			<td>Powder Diffraction Evaluation Software</td>
		</tr>
	</tbody>
</table>

x-ray powder diffraction in conservation science: towards routine crystal structure determination of corrosion products on heritage art objects

The crystal structure determination and refinement process of corrosion products on historic art objects using laboratory high-resolution X-ray powder diffraction (XRPD) is presented in detail via two case studies.
The first material under investigation was sodium copper formate hydroxide oxide hydrate, Cu4Na4O(HCOO)8(OH)2&#8729;4H2O (sample 1) which forms on soda glass/copper alloy composite historic objects (e.g., enamels) in museum collections, exposed to formaldehyde and formic acid emitted from wooden storage cabinets, adhesives, etc. This degradation phenomenon has recently been characterized as &#34;glass induced metal corrosion&#34;.
For the second case study, thecotrichite, Ca3(CH3COO)3Cl(NO3)2&#8729;6H2O (sample 2), was chosen, which is an efflorescent salt forming needlelike crystallites on tiles and limestone objects which are stored in wooden cabinets and display cases. In this case, the wood acts as source for acetic acid which reacts with soluble chloride and nitrate salts from the artifact or its environment.
The knowledge of the geometrical structure helps conservation science to better understand production and decay reactions and to allow for full quantitative analysis in the frequent case of mixtures.

High resolution XRPD was used to determine the previously unknown crystal structures of two long-known corrosion products on historic objects. The samples were taken from two museum objects and carefully grinded before they were sealed in transmission and capillary sample holders (Figures 6, 7). Standard measurements using a state of the art laboratory high resolution powder diffractometer in transmission and Debye-Scherrer geometry using monochromatic X-rays were perform...

Watch this Scientific Journal Video about X-ray Powder Diffraction in Conservation Science: Towards Routine Crystal Structure Determination of Corrosion Products on Heritage Art Objects at JoVE.com

X-ray Powder Diffraction in Conservation Science: Towards Routine Crystal Structure Determination of Corrosion Products on Heritage Art Objects

Modern high resolution X-ray powder diffraction (XRPD) in the laboratory is used as an efficient tool to determine crystal structures of long-known corrosion products on historic objects.

The crystal structure determination and refinement process of corrosion products on historic art objects using laboratory high-resolution X-ray powder ...

The overall goal of this method is to gain knowledge of the crystal structure of micro and nano crystal and corrosion products to better understand production and decay reactions of heritage art objects and to allow for full quantitative analysis of mixtures. This method can help answer key questions in the field of conservation science such as how the art object has been produced and why is it corroded. The main advantage of this technique is that it does not require single crystals but only small amounts of micro crystal and powder.Though this method can provide insight into conservation science it can also be applied to other fields such as material science, inorganic chemistry or metallogy. We found that the idea for this method when we investigated at a gradation phenomenon which recently has been characterized as glass induced metal corrosion. Demonstrating sample preparation and data collection will be Ms.Stefani, a chemical technical assistant from our laboratory.Under a digital microscope carefully pick less than one milligram of sample one from opaque blue green cabochons on a historic clasp using a fine needle. Following this, grind the sample carefully with a pestle in a small agate mortar. Distribute the sample between two thin x-ray transparent polyamide foils and mount them on a transmission sample holder with an eight millimeter diameter central opening.Fix the transmission sample holder on the theta circle of a diffractometer. Measure the sample for 20 hours from five to 85 degrees two theta, with a step width of 0.015 degrees two theta in transmission mode. Turn rotation on in order to achieve better particle statistics.The next step is to perform an automatic peak search using the first and second derivatives of Sovietske Golle polynomials of low order. First start the software program by double clicking the icon and then click Load Scan Files. Using the pull down menu select xy data files and then double click on the appropriate file.Now expand the range of the file. Click on the Emission Profile tab, select Load Emission Profile and choose the desired profile. Next click the Automatically Insert Peaks button and unclick Remove K Alpha 2 Peaks, after setting the Peak Width to 0.12 set the Noise Threshold to 1.74 and press the Add Peaks button.Zoom in on the pattern, move to the desired section of peaks and then open the peak details window. Set the peaks by pressing the left mouse button. Next click on Peaks Phase.Mark all peaks yellow by clicking on Position and then left click in the yellow marked column, copy the selection and select Create Indexing Range. Deselect the range and select Range Indexing. Then select all bravais lattices.Following this press the Run button. And Yes to keep indexing solutions. Press the Solutions button and then highlight the first solution by left clicking button one.Now right click on the highlighted solution and copy the selection. Deselect Range Indexing and then select the range. At this point press Add hkl Phase, expand the range and then expand hkl Phase.Under Indexing Details, choose Paste Indexing Details. Under Background, change Order to eight and then select 1/X Bkg term. Next click Instrument.After setting the primary and secondary radii to 217.5 mm, select Receiving Slit Width under Point detector. Under Full Axial Model, set the source, sample, and RS length to six mm. Now click Corrections and choose 0 error.Choose LP factor and set the value to 27.3. Then click Miscellaneous and set Convolution Steps to 2. Select Start X and set the value to eight, then choose Finish X and set the value to 75.Under Click Peaks Phase choose Delete Peaks Phase and click Yes. At this point click hkl Phase and choose Microstructure. After selecting Cry size L choose Cry size G, select Strain L, choose Strain G and then press the Run button.Finally create a list of brag peaks suitable for charge flipping. For crystal structure determination use the method of charge flipping supported by the inclusion of the tangent formula to find the positions of most of the heavier atoms. First under File select Close All and click Yes.Under Launch, select Launch Kernel. From the Launch pull down menu, select Set INP file and then select the prepared input file. Now press the Run button and after approximately 20, 000 cycles press the Stop button and click OK.Following this press the temporary output window displaying selected atoms button and then press the Cloud options dialog button.Set N to pick to 45. Choose width symmetry and press the Pick button. Copy the temporary output, save it to a text file and close the charge flipping graphics window.The next step is to apply the global optimization method of simulated annealing to find the positions of all missing non hydrogen atoms. From the launch pull down menu select Set INP file and then choose the prepared input file. Press the Run button and after several thousand cycles press the Stop button and click Yes.The final step is to turn off simulated annealing and switch to the Reitfeld refinement mode by commenting out the appropriate command. Under Launch choose Set INP file and select the prepared input text file. Finally press the Run button and click Yes.High resolution X-ray powder diffraction was used to determine the crystal structures of two long known corrosion products on historic objects. Standard measurements using a state of the art laboratory high resolution powder diffractometer in transmission and Debye Scherrer geometry using monochromatic x-rays were performed. Crystal structure determination of sample one was performed by iteratively combining reciprocal and direct space methods with Difference Fourier analysis.The determination of the crystal structures of these compounds confirms the exact composition, improves our understanding of the decay mechanisms and allows full quantitative phase analysis of corrosion products. Once mastered this technique can be done within one day if it is performed properly. Following this procedure other methods like DTA, Raman Spectroscopy and EDX can be performed in order to get complimentary and additional information concerning composition, bonding, possible phase transitions and stability.After watching this video you should have a good understanding of how to prepare samples, record appropriate powder diffraction data, perform data reduction and determine the crystal structure of micro crystalline material. After its development this technique will pave the way for researchers in the field of conservation science and it is non destructive, fast and easy to use.

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15.7K vistas.  Max-Planck-Institute for Solid State Research. The overall goal of this method is to gain knowledge of the crystal structure of micro and nano crystal and corrosion products to better understand production and decay reactions of heritage art objects and to allow for full quantitative analysis of mixtures. This method can help answer key questions in the field of conservation science such as how the art object has been produced and why is it corroded. The main advantage of this technique is that it does not require single crystals but only...