Desenhos Antigos Em Português

Working with vintage technical drawings from Portuguese-speaking sources

Old drawings in Portuguese — desenhos antigos em português — show up everywhere if you work in restoration, heritage conservation, or mechanical archiving. They're not a single style. They're whatever the draughtsman was following at the time: ABNT standards that predated the current NBR 10067, hand-drafted orthographic projections, watercolour renderings on onion skin, or carbon copies of shop-floor diagrams from the 1960s. The challenge is usually deciphering the annotations, not the geometry. The reliable sources are fragmented. University engineering libraries in São Paulo, Rio, and Porto have bound collections of final project drawings going back to the 1940s. INPI holds old patent illustrations, many of which are technically drawings with Portuguese annotations. Municipal archives in cities with colonial heritage — Ouro Preto, Salvador, Recife — keep architectural plans for public buildings. There are also scattered listings on OLX and Mercado Livre, usually sold in bulk as "lots" without proper descriptions, so you end up buying 40 sheets and only three of them are actually useful. For digital access, the Biblioteca Nacional Digital has some collections, though their resolution varies. A few engineering faculties upload scanned theses that include original drawings, and the Portal da Pesquisa CAPES can sometimes surface full-text theses with appendixes containing high-quality scans.

Reading the drawings themselves

The first thing to check is the standard being referenced in the drawing header. If it says NBR, look at the date. Pre-1980 NBR standards used different tolerance conventions and projection angles than what you'd expect today. Some draughtsmen in the 1950s and 60s used first-angle projection even though the Brazilian standard had already shifted toward third-angle in certain industries. If the drawing doesn't explicitly state the projection method, check the position of the side view relative to the front view — that tells you everything. Annotations are the harder part. Many drawings from the 1940s through 1970s were done in cursive Portuguese by hand. The word for "roughness" (rugosidade) was often written in abbreviated forms that look nothing like the modern textbook version. Finish marks on surfaces — those little hatch symbols — followed conventions that varied between workshops. A diagonal line meant one thing in a São Paulo machine shop and something slightly different in a Rio foundry. Scale notation is another trap. Older drawings sometimes list the scale as a ratio and sometimes as a fraction, and the fraction format is ambiguous about whether it's metric or imperial. I spent three days trying to reverse-engineer a 1958 layout for a factory floor in Campinas before realizing the scale was given in inches to feet, not millimetres to metres. The dimension numbers themselves were in millimetres, which was common practice — mixing systems without declaring it.

Preservation and digitisation

These drawings are on paper that is actively degrading. Onion skin from that era is acidic and brittle. Blueprints — the diazo process ones — tend to have a purple or blue tint that fades to white if exposed to light, and once faded, the information is gone. sepia prints are more stable but the image can crack along fold lines. Scanning them is straightforward but requires care. Use a flatbed scanner at 600 DPI minimum. Skip the automatic colour correction — the scanner software will try to "restore" the faded blue to white and destroy the drawing in the process. Scan in TIFF, not JPEG. If the drawing is folded, photograph it instead with even lighting and a polarising filter to reduce glare. Do not attempt to flatten a 60-year-old fold crease by pressing it under weight. It will crack along the fibre lines and you'll lose detail.

A practical problem I ran into

I was cataloguing a set of mechanical drawings from a defunct textile machinery manufacturer in Uberlândia, dated around 1972. The part drawings included what looked like inconsistent tolerance callouts — some dimensions had ±0.05, others had no tolerance at all. Standard practice would assume the un-toleranced dimensions were to the general tolerance stated in the title block. But the general tolerance was written in a shorthand I couldn't immediately parse: "IT 12" referenced a standard that didn't exist in that form in Brazil at the time. The draughtsman was actually referencing DIN 7168, a German standard that was widely used in Brazilian engineering until the ABNT fully adopted ISO tolerances in the late 1970s. The workaround was to cross-reference the notation against a table in the 1968 ABNT NBR 6155, which acknowledged the DIN system for transitional use. Without that connection, the tolerances would have been misread entirely. Assuming modern standards apply retroactively. A drawing from 1965 was not made to 1965 standards necessarily. Many engineers copied formats from older American or European manuals without updating the reference. Always check the material specification dates, not just the drawing date. Tracing over faded originals. It's tempting to redraft a faded drawing by hand to make it usable. Don't. You'll introduce errors that didn't exist in the original, and you lose the ability to verify your work against the source. Digitise first, annotate digitally second.

Ignoring the revision blocks. Old drawings often have revision history stamped or handwritten in a corner. These revisions sometimes contradict the main drawing because a later change wasn't fully propagated. I've seen cases where the revision block showed a hole pattern that was relocated, but the body of the drawing still showed the original positions. Always read the revision block before trusting any dimension. If you're working with large quantities of these drawings and need a management system, simple spreadsheet tracking with scan links works fine for hundreds of items. Beyond that, you'll want something with OCR capability for the Portuguese annotations, though off-the-shelf OCR struggles with handwritten cursive from that era. Dedicated archival software like Aeon or a custom SQLite setup with image thumbnails handles it adequately.