In financial results for the six months to September 30, 2012, the business said net assets had grown from £229.4 million to £440.8m.
Earlier this month, a Better Capital fund used a special purpose vehicle to buy the debt of troubled ATH.
ATH, which employs around 300 people with many of its staff at mines in Scotland, is now working with accountancy firm KPMG on a sale or restructuring of the business.
The venture firm has interests in businesses including fashion retailer Jaeger, stationery wholesaler Spicers, luxury boat-maker Fairline and publisher Reader's Digest.
Chairman Richard Crowder said: "The board is of the view that the level of potential deal flow will continue in the short to medium term, and that this will provide appropriate opportunities for the Better Capital Funds to invest selectively in businesses with good prospects for successful turnaround.
"Market conditions for most portfolio companies remain challenging and are predicted to be for some time yet.
"However, the track record of Better Capital investing in and turning around troubled businesses is expected to yield attractive exits."