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<p>[QUOTE=&quot;2manybooks, post: 4311245, member: 8267&quot;]The map with the blue lines was probably made with the diazo process, common between 1940s - 1990s.</p><p><br /></p><p>&quot;...in the 1940s, blueprints were replaced by diazo prints, aka whiteprints or bluelines. [In contrast to cyanotype blueprints, which had white lines on a blue background], diazo prints had blue lines on a white background. They were easier to read and faster to make. The process was simple, the machines were not overly expensive for reprographic companies and didn’t need extensive maintenance. For decades, bluelines were the way to make copies of architectural drawings.&quot;</p><p><a href="https://www.oncenter.com/blog/article/transitioning-to-the-digital-age/" target="_blank" class="externalLink ProxyLink" data-proxy-href="https://www.oncenter.com/blog/article/transitioning-to-the-digital-age/" rel="nofollow">https://www.oncenter.com/blog/article/transitioning-to-the-digital-age/</a>[/QUOTE]</p><p><br /></p>

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