fonts-config/31-metric-aliases-bw.conf

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
	<!-- according to infinality database, e.g. Helvetica or Nimbus Sans L
             are not well hinted. Fall back to Liberation Sans instead, when
             black and white rendering was chosen. -->
        <match target="pattern">
		<test name="search_metric_aliases">
			<bool>true</bool>
		</test>
                <test name="force_bw">
                        <bool>true</bool>
                </test>
		<!-- Helvetica represents group here as defined in 
                     30-metric-aliases.conf -->
                <test name="family">
                        <string>Helvetica</string>
                </test>
                <edit name="family" mode="append" binding="same">
                        <string>Liberation Sans</string>
                </edit>
        </match>
        <match target="pattern">
		<test name="search_metric_aliases">
			<bool>true</bool>
		</test>
                <test name="force_bw">
                        <bool>true</bool>
                </test>
       		<!-- Times represents group here as defined in 
                     30-metric-aliases.conf -->
	         <test name="family">
                        <string>Times</string>
                </test>
                <edit name="family" mode="append" binding="same">
                        <string>Liberation Serif</string>
                </edit>
        </match>
        <match target="pattern">
		<test name="search_metric_aliases">
			<bool>true</bool>
		</test>
                <test name="force_bw">
                        <bool>true</bool>
                </test>
		<!-- Courier represents group here as defined in 
                     30-metric-aliases.conf -->
                <test name="family">
                        <string>Courier</string>
                </test>
                <edit name="family" mode="append" binding="same">
                        <string>Liberation Mono</string>
                </edit>
        </match>
</fontconfig>