# The Science of Perfect Picture Framing
A passepartout (or mat board) is not merely decorative cardboard — it is the breathing space that allows your artwork to exist independently from its frame. This calculator gives you the exact dimensions to cut your mat, ensuring the artwork is optically centred or balanced within the frame to professional gallery standards.# Why Bottom Weighting Works
The optical center illusion
The human eye perceives the geometric vertical center of a rectangle as being slightly lower than it actually is. Artwork framed with perfectly equal top and bottom margins appears to be "falling" or sinking.
Bottom weighting corrects this by making the bottom margin 5-15% wider than the top. The artwork is lifted optically and appears perfectly centered — a technique used in every professional gallery worldwide.
# Conservation Mat Board: Why Materials Matter
Conservation board versus standard mat board
Standard wood-pulp mat boards contain lignin, which breaks down over time releasing acetic acid. This causes the characteristic brown foxing and yellowing that permanently destroys artwork. Conservation-grade mat board (alpha-cellulose or cotton rag) is pH-neutral and buffers against external acids, protecting artwork for decades.
# Professional Measuring Tips
Measure the rebate, not the face: If you already have the frame, measure the inner rebate from the back, not the front glass opening. The mat must fit the rebate precisely.The safety overlap: The mat window should be slightly smaller than the artwork (approximately 5mm per side) so the image cannot slip through the opening.The golden rule of matting
Never use less than 5cm (2 inches) of margin if you want the artwork to breathe. Generous margins signal quality and elevate even modest pieces to gallery status. A wide white mat transforms a small watercolour into a museum exhibit.