CDG Quality Control & Process Improvement 2 — Questions and Answers
Question 1: When a grading laboratory implements a blind re-grading protocol, what is the primary quality control objective?
- Reduce grading time per stone
- Eliminate grader bias by preventing access to prior results (Correct answer)
- Train new graders on established grades
- Standardize lighting conditions across workstations
Correct answer: Eliminate grader bias by preventing access to prior results
Blind re-grading prevents graders from anchoring to previous results, isolating true consistency and eliminating confirmation bias.
Question 2: A diamond consistently receives VS2 clarity grades internally but is returned from clients graded SI1 by a major lab. Which corrective action addresses the root cause?
- Adjust internal grade standards upward by one sub-grade
- Conduct calibration sessions using GIA or AGS master comparison stones (Correct answer)
- Retrain only the grader who handled the stone
- Increase magnification from 10x to 20x for all clarity grading
Correct answer: Conduct calibration sessions using GIA or AGS master comparison stones
Calibration against industry-recognized master stones aligns internal standards with external benchmarks, addressing the systemic discrepancy.
Question 3: In a Pareto analysis of grading errors, which category of defect should receive priority attention first?
- The error type that occurs most frequently among junior graders
- The error type representing the largest cumulative percentage of total defects (Correct answer)
- The error type with the highest individual severity score
- The error type most recently introduced to the workflow
Correct answer: The error type representing the largest cumulative percentage of total defects
Pareto analysis prioritizes the vital few causes that account for the majority (typically 80%) of total defects.
Question 4: Which diamond grading scenario best illustrates a Type I error (false positive) in a quality inspection process?
- Passing a VS2 diamond that is actually SI1
- Rejecting a flawless diamond as having an inclusion (Correct answer)
- Accepting a diamond with a cloud inclusion as eye-clean
- Failing to detect a feather inclusion under 10x magnification
Correct answer: Rejecting a flawless diamond as having an inclusion
A Type I error (false positive) occurs when a good item is incorrectly rejected — here, flagging a flawless stone as flawed.
Question 5: A grading lab notices that color grades cluster tightly on Monday mornings but spread widely on Friday afternoons. What process variable is most likely responsible?
- Variation in the diamond supply from different rough sources
- Grader fatigue affecting visual acuity and decision consistency late in the week (Correct answer)
- Inconsistent client documentation arriving with Friday shipments
- Fluorescence effects that are stronger under weekend lighting conditions
Correct answer: Grader fatigue affecting visual acuity and decision consistency late in the week
Grader fatigue is a well-documented human factor that degrades the precision and repeatability of visual assessments over long work periods.
Question 6: What does a control chart's 'R-chart' (range chart) measure in a diamond grading context?
- The average grade assigned across a batch of stones
- The consistency (spread) of grades within subgroups over time (Correct answer)
- The rate of customer complaints per shipment
- The ratio of SI to VS grades produced per grader
Correct answer: The consistency (spread) of grades within subgroups over time
The R-chart tracks variability (range) within subgroups, revealing whether the grading process is consistently tight or erratically spread.
Question 7: When introducing a new inclusion mapping software to graders, which Six Sigma phase involves testing the tool on a pilot batch before full deployment?
- Define
- Measure
- Analyze
- Improve (Correct answer)
Correct answer: Improve
The Improve phase of DMAIC is where validated solutions are piloted and implemented based on root-cause analysis findings.
CDG Quality Control & Process Improvement 2
When a grading laboratory implements a blind re-grading protocol, what is the primary quality control objective?