On Wednesday, the Dow Jones Industrials (DJINDICES:^DJI) built on yesterday's modest gain, rising about 30 points as of 11 a.m. EDT. Investors were generally upbeat about the prospects for earnings season, as the unofficial beginning came last night in the form of impressive results for the aluminum industry's biggest U.S. player. Yet even though those results would seem to indicate better times ahead for materials and industrial stocks, Caterpillar (NYSE:CAT) and General Electric (NYSE:GE) aren't seeing nearly the positive impact that aluminum-stock investors enjoyed this morning. That raises the question of whether investors in Caterpillar and GE have confidence that conditions truly are improving, especially in key markets.

Source: General Electric.

General Electric actually lost 0.4% this morning, which seems particularly odd given that it shares key customers with suppliers in the aluminum industry. Aerospace has become an increasingly important part of both the Dow Jones Industrials' overall industry exposure and General Electric's business in particular. With huge increases in aircraft production leading to higher demand for both custom-made aluminum-fabricated products and General Electric's jet engines, the conglomerate expects plenty of growth potential from the industry going forward. Yet General Electric shareholders must feel some consternation that the wide range of GE's businesses gives them exposure both to massive opportunities but also big risks involved in trying to make the most of those opportunities. In the long run, General Electric needs accelerating economic growth both in the U.S. and worldwide in order to make the most of its potential.

Meanwhile, Caterpillar did post a modest 0.3% rise, building on its gain yesterday stemming from strong performance in emerging markets such as China. For the aluminum industry, China has had a mixed impact, with demand from its growing economy helping to support prices but extensive supply also coming into the market from domestic aluminum manufacturers. Caterpillar, on the other hand, has to worry not only whether economic growth in China will accelerate, but also whether its underpinnings are sustainable, especially given rising concerns about what some have called a credit bubble. If China falls, it will have huge implications for Caterpillar and for the Dow Jones Industrials on the whole.

The beginning of earnings season might sound propitious for the Dow Jones Industrials. But even if the Dow responds well, that doesn't mean that all of its components will follow suit. Until Caterpillar and General Electric can address their company-specific issues, they might not add to the Dow's gains as much as many investors would hope.

Dan Caplinger owns shares of General Electric Company. The Motley Fool owns shares of General Electric Company. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.