The first step in a barré investigation is to observe and define the problem. Barré can be the result of physical causes that can usually be detected, or it can be caused by optical or dyeability differences that may be nearly impossible to isolate in the fabric. Barré analysis methods that help to discriminate between physical barré and barré caused by other reasons include Flat Table Examinations, Light Source Observation, and the Atlas Streak Analyzer.
Flat Table Examination
For a visual barré analysis, the first step is to lay a full-width fabric sample out on a table and view both sides from various angles. Generally, if the streaky lines run in the yarn direction that is in the course direction, apparent color differences can be seen by looking down at the fabric in a direct visual line with the yarn or course direction, and the defect can be positively identified as a barré defect. Viewing the fabric with a light source in the background will show if the barré is physical.
Light Source Observation
After completing an initial Flat Table Examination, a Light Source Examination may provide further useful information. Full width fabric samples should be examined under two surface lighting conditions, ultraviolet (UV) and fluorescent light. Observations that should be made while viewing under lights are:
1. the frequency and width of the barré,
2. whether the streaks are dark or light, and
3. the total length of pattern repeat.
Ultraviolet light, commonly referred to as "black light," allows the presence of mineral oils to be more easily detected, due to their radiant energy (glow). When observed under UV light, fabrics with streaks that exhibit glow suggest improper or insufficient preparation. A change in composition or content of oil/wax by the spinner or knitter without appropriate adjustments in scouring can create this problem. Fluorescent lighting simulates the mode of observation that is common to most inspection tables in mills and will highlight whether the barré is perceivable in an industry quality control setting.
