I have an asset in gnucash, and its value changes over time. I followed these instructions and know how to record the gains, but it's unclear to me how I record the losses. The help page describes setting up the accounts, but only an income account and no expense account is created. Does this mean that I record losses as 'negative income' in the income account?
According to the gnucash guide, losses are recorded as negative transactions against Income:Capital Gains. I've followed this model in the past when dealing with stocks and commodities. If on the other hand, you're talking about an asset which could normally follow a depreciation schedule, you might want to look at the section in the business guide dealing with asset depreciation.
It depends on whether or not you are referring to realized or unrealized gains. If the asset appreciation is realized, meaning you've sold the asset and actually collected liquidity from it, then Derek_6424246 has provided a good route to follow.
However, if the gains are unrealized, meaning only that the current value of the underlying asset(s) have increased or decreased, then you might want to record this under an Income:Unrealized Gains account. One of the main distinctions between the two are whether or not you have a taxable event (realized) or just want to better track your net worth at a given time (unrealized).
For example, I generally track my retirement accounts increase in value sans interest, dividends and contributions, as income from an Income:Unrealized Gains account. I can still reconcile it with my statements, and it shows an accurate picture for my net worth, but the money is not liquid nor taxed and is more for informational purposes than anything.
And no, I don't create an additional Expense account here to track losses. Just think of Unrealized Gains as an income account where the balance will fluctuate up and down (and potentially even go negative) over time.