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Difficulty: HardRecognizing Explicit Cause and Effect

Medieval stained glass windows owe their vibrant, translucent colors to metallic oxides suspended in a silicate matrix. However, windows crafted in northern Europe between the tenth and fourteenth centuries are uniquely susceptible to a destructive weathering process known as 'crizzling.' Unlike Roman glass, which utilized soda-rich plant ash as a flux, medieval glassmakers in landlocked regions substituted wood ash, which is rich in potash (potassium carbonate). While potash lowered the melting temperature of silica during fabrication, it also produced a glass structure with significantly lower chemical stability. When exposed to atmospheric moisture, the potassium ions within the glass matrix undergo ion exchange with hydrogen ions in rainwater. This leaching process leaves behind a silica-rich gel layer on the glass surface. Crucially, as this gel layer dehydrates during dry spells, it contracts at a different rate than the underlying intact glass, causing microscopic fractures to propagate inward. Over time, these micro-fissures refract light in multiple directions, transforming once-luminous stained glass into an opaque, chalky white substance and eventually causing the glass to crumble entirely under its own structural stress.

According to the passage, the propagation of microscopic fractures inward is directly caused by which of the following?

  1. A
    the ion exchange between potassium ions in rainwater and hydrogen ions within the glass matrix
  2. B
    the refraction of light in multiple directions, which accelerates the dehydration of the surface gel layer
  3. the differential contraction rate between the dehydrating surface gel layer and the intact glass underneathAnswer
  4. D
    the use of wood ash as a flux, which lowers the melting temperature of silica during fabrication

Answer

The correct answer describes the differential contraction rate between the dehydrating surface gel layer and the intact glass underneath.
The passage explicitly states that as the silica-rich gel layer dehydrates, it contracts at a different rate than the underlying intact glass, causing microscopic fractures to propagate inward. This unequal rate of contraction directly drives the propagation of the fissures.

Step-by-Step Solution

1
Locate the mention of microscopic fractures in the passage.
The passage mentions 'causing microscopic fractures to propagate inward' in the seventh sentence.
Identifying the location of the target effect allows us to trace its stated cause in the immediate context.
2
Analyze the causal relationship described in that sentence.
The sentence states that as the gel layer dehydrates, it contracts at a different rate than the underlying intact glass, causing the fractures to propagate.
This establishes the explicit cause of the fracture propagation.
3
Match this cause to the options and eliminate distractors.
The option describing the differential contraction rate matches the passage's explanation, while other options distort facts, confuse unrelated details, or reverse causality.
Ensures the selected option aligns with the literal details and causal logic of the passage.

Key Concept

Recognizing explicitly stated cause-and-effect relationships within a passage.
Estimated Time:2m 0s
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Topics

Recognizing Explicit Cause and Effect

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