Journal of Archaeological Science: Reports 47 (2023) 103817 2352-409X/© 2022 Elsevier Ltd. All rights reserved. A pXRF analysis of historic brick chemical data throughout the lake Michigan Morainic region, United States Lauren D. Finnigan * , Mark Golitko University of Notre Dame, 296 Corbett Family Hall, Notre Dame, IN 46556, USA A R T I C L E INFO Keywords: Historic preservation Masonry repair Cream City Midwest Archaeology ABSTRACT Prior research has identifed and grouped localized brick samples utilizing portable X-ray fuorescence (pXRF). This work asks whether historic brick samples across a multiple-state regional area can be reliably grouped based upon pXRF data. To answer this, pXRF readings (n = 718) were taken from sites or extant buildings (n = 36) in Milwaukee, Wisconsin; Chicago, Illinois; Hobart, Indiana; South Bend, Indiana; The University of Notre Dame, Indiana; and Zeeland, Michigan. Results indicate distinct chemical groupings that correspond with and represent different brick production sites. In some cases, it is possible to identify the use of brick of more than one chemical type within the same structure. This work is important because of the historic signifcance of bricks as an artifact class. A rich history of brick production has become a crucial factor in the community identity for many of these sites and the results of this project indicate that matching brick samples found in archaeological sites to their production site with pXRF is promising. The results from this work also indicate that historic bricks that are to be reused for contemporary repairs and construction projects can be accurately sourced based upon chemical data supplied by pXRF analysis. 1. Introduction This paper is the result of an extensive analysis into the material properties of historic brick produced primarily around the lower lobe of Lake Michigan. Bricks were produced in massive quantity through this area in the late 19th and early 20th centuries, providing material for explosive industrial and urban growth, and for co-constructing the built environments of millions of people. A thorough understanding of the chemical composition of these bricks allows researchers to map the presence of various distinct brick types and to reconnect their regional material history. Historic bricks have achieved an importance that transcends their indexical value to the communities that produced them. In the past 150 years some culturally signifcant brick buildings have suffered damage from the multiple freeze–thaw cycles endemic to the lower Great Lakes. The Rust Belt is considered a “severe weathering” area with one of the higher weathering indices in the country (Gross and Plummer 1973, 12), and because of the variance in material response to external cold contraction or heat expansion, it is necessary to utilize similar bricks when performing these repairs (L´ opez-Arce et. al. 2003, 59; Plumridge and Meulenkamp 1993, 200; Schuller et. al. 2012, n.p.). If a brick or masonry unit expands and contracts at different rates than the bricks around it, this can lead to gapping, cracks, and eventual masonry failure. This makes the accurate identifcation of brick samples increasingly important to properly preserve these buildings or sites. This project utilized pXRF to obtain chemical data on over 700 (n = 718) bricks from 36 buildings in six cities across four states (Wisconsin, Illinois, Indiana, Michigan, see Fig. 1), including ex-situ, in-situ, com- mon, and face bricks. Bricks present unique challenges in chemical sourcing, including variable clay sources, unavailable historic docu- mentation, and the capacity for mobile chemicals to leach into their porous structure, especially in heavily industrialized environments. Structures in the Rust Belt are especially susceptible to these industrial impacts, and, with the acute need for replacement bricks for repairs, the requirement for an accurate data set and reliable chemical analysis method becomes increasingly important. The results from this work provide the largest and geographically broad assessment to date of historic brick using pXRF, determining that large-quantity, time-sensi- tive analyses across regional areas is possible. It is intended to demonstrate the value of brick as an artifact class as well as the capability of portable X-ray fuorescence (pXRF) data ob- tained from sites across a broad, multi-state, geographic area (~150 * Corresponding author. E-mail addresses: pfnnig1@nd.edu (L.D. Finnigan), mark.l.golitko.1@nd.edu (M. Golitko). Contents lists available at ScienceDirect Journal of Archaeological Science: Reports journal homepage: www.elsevier.com/locate/jasrep https://doi.org/10.1016/j.jasrep.2022.103817 Received 1 November 2021; Received in revised form 25 November 2022; Accepted 28 December 2022